This is an age-old question about training in general. It's generalized as the "Breadth vs. Depth" dilemma.
A "Depth First" training philosophy would prefer to train in a small number of things, but teach them deeply before moving onto other things. This way, you get really good at everything you learn, but you won't have a good understanding of the broader range of knowledge, at least not for a very long time.
Whereas, a "Breadth First" training philosophy would prefer to train in a large number of things, but obviously that means not spending much time on any one thing before moving on to the next. This way, you get a really good idea of the range of different things to learn, but you won't get a good understanding of anything in a deep way for a very long time.
Which is better for jiujitsu? I observe that most jiujitsu schools have success teaching more broadly at first, showing the student a good overview of the system before coming back to certain topics in order to gain a deeper understanding of them. So for most jiujitsu schools, it's more of a breadth first philosophy at first, and then it changes to a depth first philosophy, sometime after blue belt has been reached.
That's my impression, but I could be wrong.
For martial arts in general, or really anything you want to learn, this is probably the training philosophy with which most people do best in the long term. Teach broadly at first, and then later on teach more deeply.
But there's more to learning than that. Learning must involve repetition. That's how human minds learn. We have to repeat it a lot at first in order to learn it. And we have to come back to it again and again later on. This will go on until we feel we no longer need to repeat it as often, but we'll probably never be able to stop repeating it entirely without forgetting it or without letting our skills deteriorate.
It turns out that there's a learning method that memory experts have discovered for optimally remembering anything in general. They call it the "Spaced Repetition" method, which you can read about here:
Now, most of the time when memory experts are talking about Spaced Repetition, they're talking about memorizing lots of data. It's about pure memorization. For example, learning new vocabulary words or new languages. But it turns out it can be applied to pretty much anything, including martial arts training.
Spaced Repetition gives you a way of training so that you never forget it, and it's always fresh in your mind. At the same time, it lets you continue to learn more and more over time without overwhelming you.
So for example, you might learn a technique on Monday in your jiujitsu class. You repeat it 100 times that day to really drill it in. Then on Tuesday you come back and repeat it just 70 times. Then you skip Wednesday and come back to it on Thursday and repeat it just 50 times. Then you skip Friday and Saturday and come back to it on Sunday to repeat it just 30 times. Then you skip Monday, Tuesday, and Wednesday and come back to it on Thursday to repeat it just 20 times. Etc.
Each time you repeat it, you can repeat it a smaller number of times than the previous day you did it. And each day you practice it, there can be more days in between that you are not practicing it. Over time, you might only have to practice it once a month or once every two months, and repeat it only a small number of times that day.
Why does this matter? It matters because there's a lot of stuff to learn! It makes no sense to repeat everything you've learned the same number of times and do it everyday. You would wear yourself out, and you'd run out of partners. So you have to be smart about it. Time is limited.
The stuff you just learned will need to be repeated a lot more than stuff you've learned a year ago and have already practiced a lot. So your time will be spent mostly (but never entirely) on repeating stuff you've only recently learned.
A good martial arts instructor will be aware of this, even if he/she doesn't know the actual phrase, "Spaced Repetition". They know what topics are fresh in their students minds and which aren't. So they continuously refresh topics that are beginning to deteriorate. We don't ever want our skills to deteriorate.
Now, the trouble is that this must be tailored to the individual, yet teachers are teaching lots of people at the same time. So teachers will never be perfect at this. Some students may come in only once a week, for example. Others are there every day of the week. How do you teach classes when your students are all different? It's tricky, and it's going to come down to the teacher's awareness of his/her students.
As a student, that should tell you something. It should say that you probably want to manage your own practice outside of class with your own personalized Spaced Repetition method. You might keep track of all the techniques or topics you've been taught in class. Each time you practice a topic, you record when you practiced it, how many times you repeated it, and whether or not you ended the practice feeling like you were successful. Then you decide how many days should go by before you come back and practice it again as well as how many times it should be repeated on that day. Schedule it, and keep to the schedule. Do this with every topic you have.
Again, how many days go by before you practice something again as well as how many times you would repeat it on that day is determined by how you feel about the last time you practiced it. If you feel your skill at that technique is getting worse, then you might decrease the number of days between practicing it and increase the number of times you repeat it on the day you practice it. If you feel your skill at it is getting better or staying the same, that means you can increase the number of days between practicing it and decrease the number of repetitions when you practice it again.
This is a feedback loop. It requires you to keep a journal and continuously update your schedule. There might be apps either for cell phones or for desktop PC's that allow you to do this on computer. But it's fairly easy to do with just pen and paper.
And by the way, for most people, this isn't something they care to do even if they know about it. Only the most serious students will practice this way. But most serious students I've seen practice a lot more than they need to. They over-practice. They don't know about Spaced Repetition, so they end up repeating things more than they need to and more often than they need to. They might also neglect to practice the older stuff they were taught, preferring to rigorously practice the new stuff they've been taught. That results in deterioration over time.
Time is the reason why this matters. There's too much to learn, yet we all have just a limited amount of time in which to learn it. It makes sense to use however much free time you have in the most optimal way.
My thoughts anyway.
Hope that helps.