Well DAW builders would hardly provide the function if it was useless!If you have Waveforms completely out of whack with one another... you're doing something wrong when you're recording them. If you can't see your Waveforms (i.e. they are all too small, Shift + Up Arrow in Reaper will increase them until you can see them properly, other DAWs should have similar Waveform functions). "Normalizing" isn't something you should really be doing, it should be fixed at the source in my eyes.
I don't 'do' music, that is son's department but very often I get recordings from people chasing very low level noises, hums and such. They can be down at -50dBFS so I just bang them through 'normalize' and then I can hear and 'see' them.
The function just make the signals bigger as almost everyone has said. If peeps just want to tweak a fader, that is fine as well. In fact in Samplitude you don't need to do either. Just click on the track line and push!
Dave.