It's important to note that computers don't really understand dash dancing very well, but end up making up for it by having inhuman reaction times (literally).
There's this concept called burst range in fighters, meaning the range at which a character can put a hitbox before the opponent could possibly react. Burst range changes depending on position and understanding burst range is a large part of understanding how to get the "first hit" in any given conflict.
Since CPUs don't really have a human reaction time, they kinda don't care about your burst range, and can react to anything no matter what. The only reason they get hit is they tend to choose unsafe options and/or just choose to get hit. As such CPUs in particular teach very bad neutral game habits, since they get hit by lots of things humans wouldn't simply because their option choices are poor or they randomly choose not to block, and since they aren't afraid of burst range, whereas humans are. It's a bad combination, since some of the worst options against humans work well against CPUs and some of the best options against humans don't work against CPUs.
Other things to look out for:
-CPUs sometimes have insane, unrealistic smash DI.
-CPUs perfect shield reflect more than even the best human players.
-CPUs tend to be predictable and/or terrible at recovering, teaching you to cover options that humans would either never choose, or would only choose as a mixup
*Note: the above was copied and edited from a post I made in an earlier, similar thread
A good way to practice against CPU's is to set their level to 1-4 so that they don't really hit you, but so they move and you can simulate / pretend you are in particular situations and practice what you might do (which is called "shadow boxing"). Iirc this is how Dr PP trains with CPUs.
