I probably have, but I use front or rear brake. Hills etc don't really have an effect for me over control of the bike.If you've parked on a hill and left the bike in first then it's easier to start in first compared to rocking it to get neutral before starting it. Also at roadwork lights you should turn off the bike, and here it's safer to leave it in first in case you're rear ended and starting in first avoids needing to go first > neutral > start > first > go.
I'm very surprised that you've never come across scenarios where starting in first is preferred.