I use a gig bag when I am playing in a small venue with little or no place to store a hard case, eg, A wedding in someones home. But I only use it for the electric guitar.The acoustics ride in comfort in a hard-shell case no matter what the venue.
The only acoustic I EVER put in a gig bag is an Applause (like an Ovation with an aluminum neck) that I gave $50 for. It's about as bullet-proof as you can get. I even sent it trans-atlantic once and it came thru as good(?) as ever.

troll