There are situations, where you loose your crew. Taking hull damage, losing ships, losing piloted fighters, salvaging and etc...
So, yes, having a few more spare crew is not a bad thing, until you able to pay them salary. Sometimes you better pay more, than find yourself at the middle of nowhere with less than skeleton crew required, especially if your main power is carriers...
Additional berthing used either on battle ships to slight increase of crew limit (not to have a logistic crew ships in your fleet) or on a crew ships to maximize crew capabilities, usually for transporting marines for raids.
So, yes, it is a useful hullmod, but if your playstile does not require that - ignore it.
P.S. Welcome to the forum.