In various (usually Kung Fu) movies & clips on YouTube, you see lots of wide swinging punches to the head. It seems to me that it could theoretically work, but that if you’re a little bit off or if the guy moves his head in a little, you’d connect with the heel of your palm, your clenched thumb, and the second-from-the-fingertips sections of your fingers. So, are wide swinging punches at all advisable in real life?
The wide swinging punches you see can be used, but there's usually some bits of context that is usually erased when you see them in movies or demonstration sets.
First, some of these movements were originally designed for weapons, not empty hands. China has a long history of weapons being banned, or of people just being too poor to afford enough weapons for everyone - but they still practiced the moves. Whether that concept was lost during the transmission for some schools, or whether they show it empty hands in public while practicing the real usage in private, depends on the particular school/lineage.
Second, when they are designed for empty hand attacks, the wide swings are not your entry attacks - they telegraph too much. They're designed as followups after you've engaged in some way (got them with a jab, grabbed their guard, got them off balance...)
Third, a lot of the wide-swinging punch movements, the contact point is either the nice, thick bone protuberances at the wrist, or the forearm proper. Not only does this give you a broader contact point, it also transitions into grappling, locks, or take downs quite well. (Also, some of the swinging "punches" are actually takedowns, again, either hidden deliberately or lost through mistransmission.)
For both demonstrations and movies, wide swinging movements look great, which is why they show up a lot, even though combatively, they may be used very differently or not as much.
They could work. Lots of styles of Kung Fu use circular motions in their movements. Kenpo also uses some circular motions. They work depending on the situation and a true master of their art will be able to show how. I personally don't believe they are ideal for self defense in today's world, but when you talk about the movies the goal is to make it look nice and flashy with flow to it. Straight punching can be quite boring for a movie.
I think it is a matter of timing as always. Nevertheless Furi Tsuki (also called Furi Ush) is one of my favorite Karate techniques, as it has shown a high rate of effectiveness for me so far, and it is a very dangerous punch when correctly connected (which means you must use it with control, or not use it at all).
In Goju-Ryu Karate style at least, this technique is composed of a swinging block with one arm, while swinging the other fist down from the back, and it hits the head temple with the two main knuckles with the fist turned on it side, powered by the whole torso, both arms and shoulders, and the hip.
First, I would say that it is important, when watching a form or even partner work between two people, to be careful identifying an intended throw. It's sometimes hard even watching sparring, if a wide swinging arm was meant as a block, a strike or a missed grab or throw.
Second, I would say that many blocks in several styles are thrown as strikes with the theory (right or wrong) that any movement should try to be both. A block should culminate in a grab/off-balancing, a strike should quickly flow into a grab, throw or off-balancing. This concept often causes some "hook" punches to look a little wild when they really shouldn't be. A little sloppy.
Thirdly, A few punches I've been taught (with varying degrees of practicality) are the "hammer fist" thrown in a wide horizontal arc across the centerline, often thrown wide to clear a guard. Also, the reverse "Oh Uch" punch which goes wide and ends towards the centerline, often used with short weapons but seen open-handed as well.
Lastly, Much of what we see in performed styles are, frankly, stylized to look impressive to spectators. Arcs and circles are made very wide to represent idealized "circles" which are prized in the art or to represent an idealized posture in Eastern spiritual contexts.