Since you mentioned [e] [j] [a], I'm guessing you're talking about console roms as I think this is the convention for a lot of console romsets. I think [a] usually means an "alternate" revision of a game rather than another country, whereas [e] and [j] should be Europe and Japan respectively.
I'd say in 99% of cases, the alternate and other country roms are going to be so similar to each other that you don't need them. The games are generally identical except for maybe some different text on the title screen or in the case of some Japanese games, some in game text may be Japanese. I would just pick the version for whatever region you're from and dump the rest. Though as polaris mentioned you need to be careful about deleting a "parent" rom that the other versions need to run. I don't think console romsets usually work this way, but I have seen it, so don't permanently delete anything until you're sure you don't need it.
Hope this answers your question.
