Hmm, there's various types of editing.
Editing for *advertising time* or similar things (i.e. the AS cards and promos) is the most annoying form of editing, at least to me. This includes edits like the butchering of the ending credits and opening themes to anime series, which is *really* annoying in many cases (i.e. CN's speeding up of the end themes to Cowboy Bebop and Big O) and in some cases even alters the actual ending of the anime for no reason (the TV cut of Trigun's ending, which has led to a prevalence of inane fanfic about the characters just wandering off into the desert, grrrr)
Editing for *content* is what Marth hinted at, and another common form of editing for TV. Sometimes, the edits are things that are obviously needed for American FCC regulations (i.e. cutting out the Gren turning to face Faye unclothed scene in Cowboy Bebop, cutting out certain profane words-usually the "s" word, more rarely the "f" word since it isn't there as much in the first place). Other times, the edits are pointless (i.e. the same thing that was edited or something worse was allowed elsewhere) or made to turn something "kid-friendly" (i.e. the American TV edits of Sailor Moon, Yu Gi Oh, and Ruruoni Kenshin are examples of this, where almost *everything* that could possibly be seen as "questionable" for a 7 year old gets cut out)
I can kind of understand the FCC regulations edits, although as a writer I don't really support them, and Polycarp made a good point about the kid editing in another thread, although, I really still don't like it much *shrug*
Anyway, these are the main forms of editing. . .and some anime is edited differently (whether it is worse is your opinion) than others, as I pointed out. The American TV version of Cardcaptor Sakura ("Cardcaptors") and of Sailor Moon are fine examples of absolutely terrible TV edits, while others are simply cut for FCC issues and ad time.
Hope that was helpful