Just turned 70 last month and went for my first bike fit. Did this for a 3 reasons.
1. My height (6'3" / 190cm) puts me typically between a large and extra large frame.
2. I didn't want to mess around with trial and error for seat, stem / bars, etc - I just wanted to ride comfortably, after a few years away from biking and I'm not as flexible as I once was.
3. The bike technology had changed so much since I last did serious riding (>5K kilometres a year) I wanted to be reasonably confident that my thinking and understanding on what would work was in fact true.
I'd say the bike fit helped in some area's to clarify and confirmed what I'd been reading so I got good value but I didn't have any "Eureka" type moments. I ended up changing the seat post and stem.
Would I do it again - depends on how much I was going to spend on a bike. Big $$ then probably.