Care to do a breakdown on hitlag?
Hitlag, also called hitstop, hitfreeze, and hitpause, is basically when the game freezes the characters at the point of collision during an attack. Having the smooth arc of the character’s attack paused at that point of collision helps sell that the collision actually happened, gives the eyes a few frames to register and confirm it happened, and makes the impact seem a little more powerful, since if the guy’s fist or sword or whatever is stopped along its path, then clearly it needs a lot of force to go through the object that is being hit.
Fighting games and Smash Bros make use of this time to practical ends. The 2in1 Cancel in Street Fighter 2 exists entirely because of Hitstop. Basically, they made the first 5 frames of every single normal move cancellable to make it easier to input special moves, but the hitstop extended that cancel window since it froze the state of both characters for like 10 frames, meaning people could still cancel after the move hits. Since then it’s been a staple of Street Fighter that you can cancel moves during the hitstop period. And this is really convenient too, since the cancel takes effect at the end of the hitstop, so it always comes out during the same part of the move, helping to keep combos consistent. So now you have this large dedicated time that is pretty much exclusively there for canceling things on hit, that’s pretty damn good.
Meanwhile in Smash Bros, during hitlag as they call it, you can wiggle the stick to move around a little, called SDI or PI. This is really helpful in smash’s system for getting you out of multi-hit moves, and for surviving certain combos. Also in Smash they have characters vibrate during hitstop, either horizontally on the ground, or vertically in the air. Looks pretty cool. You don’t really notice this in-game, but you can feel it when it’s there, and when it’s missing.
In other games, like Single Player Action Games, it’s just there to look cool and improve visual comprehension. If you don’t have hitstop, like say, Dark Souls 2, then it weakens the impact of the hit perceptually, and makes it harder to tell a hit occurred. Hitsparks are also useful as additional feedback and establishing the point of contact, to make it more clear what’s going on.