For me, pretty important. My first pro quality instrument was made by a friend who wouldn't let me leave his shop without also buying a case. 5 years of hard gigging later, that case is nearly destroyed, but the instrument is still in pretty solid condition.
I also recall a guy buying a custom ESP in Knut Koupe music in MSP back in the 80's. He didn't want the case. Right after he paid, he was on his way out the front door, and a guy from the back of the music shop slammed into him, denting the fretboard and scarring the custom airbrush paintjob on the door frame. Seems the smash-er had heard he was getting a parking ticket and was running out of the store to drop another dime in the meter.
As above, I'll use a gig bag for local jam sessions, but in a car full of gear I'm much more comfortable with a hard case.