The other day I just learnt how to slip in boxing and my coach told me to transfer your weight to the leg towards which you slip. Now by doing this it makes me wonder if you're actually balanced anymore, since your weight isn't distributed evenly.
Having equal weight distribution among your feet is a naive and limited form of balance. Demonstrating balance with an uneven weight distribution, or with only one foot on the ground (or, in other contexts, with hands but not feet on the ground, or with two feet and one hand...) is a more difficult form of balance that is often appropriate and useful for particular purposes.
One can be balanced while transferring weight mostly to one foot, as long as one is in position to move out of that state in multiple directions. Doing so is useful for power production, avoiding strikes, sweeps, or takedowns, and so on.
If you only practice being balanced while perfectly upright with each foot bearing equal weight, then you will be unable to execute a large variety of offensive and defensive techniques. More frighteningly, you will be lost when, in the course of a chaotic fight, you are forced out of your perfect position. It is important to develop comfort and balance with an uneven weight distribution, even if a perfectly even weight distribution is technically the ideal position.
By keeping on your toes all the time and using small steps you should be able to avoid your slip taking you off- balance. The slip has to be long enough just to slip the punch, if it goes for much longer, it stops being a slip and you have to keep on your toes to regain balance rapidly to your new position. But if you keep on your toes, you can recover from the slip quickly enough and not lose balance.