It seems that "normalizing" would be an appropriate process to use everytime you make a recording.... but there are specific reasons you don't want to use it at all depending on the context...
As dachay2tnr, it brings the top level to Odbfs (assuming you normalize to 0dbfs)... this of course also brings the noise floor up along with the rest of the signal... something that may or may not be a problem, depending how quiet the recording was to start with.
Also, for a single song that you want to pass out, it makes sense to bring your levels up, but let's say you're doing an album... you don't want to simply normalize each track because you will destrot any natural dynamic balances between songs. The last thing you want to have happen is your soft ballad to come in as loud as the previous hard-hitting rock track....
It is a tool - useful in the appropriate context.... real easy to abuse too!!
Bruce