What kinds of things can a professional studio fix and not fix with recording/mixing/mastering?
They can't improve your guitar skills if that's what you're thinking...
Well, it all depends on the producer.
Quote by human-blasphamy
Didnt MCR do that song The Gay Parade It went like this
when I was A young boy
My father took me to the bedroom
and told me not to tell
They can make your album sound more professional and clean. But if your songs suck outside of the studio, they will still suck in the studio.
Quote by John Mayer
"'What do you do when you've seen the most stupendous, stunning, earth-shattering show of all time?' Uh...I dunno...stop using hyperbole?"

UG 83
Quote by uuuuhhhhhhhh
Shows what you know. DigiDesign Invented this wonderfull toy called Protools.

It was more of a joke...

If you wanna get "technical" then, sure it can make you sound a little better than you are.