What do you mean by that exactly? If you simply edit footage into the timeline it requires a render? Or do you mean everytime you apply any kind of effect (cross dissolve, change something on the motion tab, etc.) that it requires a render?
If you're requiring a render when simply cutting a clip onto the timeline, then you have a sequence setting problem. Specifically the sequence settings are not the same as your footage. You need them to match inorder to make the universe all good. Like Noah mentioned, with FCP 6 it will do this for you when you first drag on a clip. But if you have a 5.x version, then you need to make sure you deal with this.