In some circumstances US versions will be edited (eg: female character sprites changed, nudity removed, certain weapons missing, blood missing, etc) because for some bizzare reason the US censorship board doesn't seem to believe US citizens are capable of making informed choices for themselves, and need to be shielded from bizzare Japanese culture icons.
Although that was far more prevalent on consoles than it was on arcade hardware. But still, there are a few instances where it occured.
You'll find that the "World" version of a game will be larger than the localised ones, as the localised versions were merely a few extra sprite or text/font ROMs that sat beside the parent world version. Deleting the localised versions won't do much to save disk space. And if you don't want clones, you can easily turn off the option to display then in most front ends.