You'll get just as many "you don't need to wipe" as you will "you should do a Javaloader /wipe first"...
Those that say it isn't needed, say this because of the wipe the app loader does as part of its process of loading new code/OS to the hand held.
However a Javaloader Wipe, and even "ResetToFactory", shouldn't be discounted if your device is experiencing problems and that is why you are reloading code.