100% of the time, absolutely no exceptions. I've lost close friends to simple car accidents because they weren't buckled up. If you wear it all the time then you don't even notice it's there and it's a second nature to put it on right away.
The amount of people I knew when I was younger who just wouldn't use a seatbelt I never understood it, like its the smallest effort for a big die-less bonus.
I thought it was a dumb question too, but then we had a school assembly last year and my smart friend (who got 13 A*s at GCSE) said that he doesn't wear a seatbelt if he's on the backseat, because it's safer than the front.
Yes it's a shame an accident made me realise this tho.
I was sat in the middle seat at the back and had no belt. We go into an accident and the breaks were so hard I almost flew through the windscreen. I was 2 inches away then flew back to the back