Lorraine - it IS necessary all the time. But all the time is different on different people's hair. And all the time isn't necessarily "once every 8 weeks" or "with every relaxer" just because that's what we've always been told to do.
By limiting my trims to only when I need them (which is really only about 2x a year - for me) I stopped cutting off HEALTHY hair and allowed my length to accumulate. I understand - it sounded counterintuitive to me as well. But when you take the kind of care with your hair that we do on the board, if you really stop and evaluate your hair before you go trimming you MAY just find that you can wait. The key is also finding a stylist who won't "make up" for the trims you opted not to have by cutting 3 inches when you only need an inch, just because you didn't get one last time.
My ends are completely healthy. I have pics on the board - the thread is called "progress pics". Check 'em out for yourself.
Also have a look at Supergirl's Scissor Happy Stylist's thread - I'll try to bump it up for you - but it goes into great detail about trimming complete with why trimming WITH your relaxer is bad (I never do that anymore) etc....
Supergirl does it, Adrienne does it...I know few women with very long hair that trim every six weeks - and their lengths are no less healthy than if they did, if they take care of their hair.