Always. Though it can be hard to buckle those up with the receptacle so low in the seat - and my FAT rump!
Back in the 70's I was drive a big GM B-body with a front bench, big block 455 and Posi. I decided to try a "emergency" U turn on a vacant State highway really just for fun and driving dynamics investigation and learning.
When I attempted it, I slid over against the passenger side door across that Naugahyde bench! Luckily I was able to keep my left hand on the wheel and my left foot on the gas to pull it out of the spin.
Since then, I belt up to keep me in the seat with my road antics. Later I do it for safety too.
I did have a crash in a little Honda Accord 3 door hatch in 1983. The DS belts did nothing except rip my pants off as I flew towards the back side window. That's what happens when you hit a pole going backwards at about 40 MPH. I blame the unsafe honda seats, as the backrest's mild steel pan just folded in half above the recliner and gouged into my back. Almost killed. Then, Getting hit between the eyes with the DIN style "snap in" radio didn't help either. "WRKO coming at you with some Led Zepplin ...." SMACK!
Ouch....