Just realized my pruning cuts were too flush this whole time

Honestly, I been doing tree work for about 9 years now and never questioned how I was making my final cuts. Last month I was trimming a big maple in a client's backyard in Akron and the homeowner, who used to work for the city parks dept, stopped me. He pointed at a cut I just made and said "you're leaving no collar, that's going to rot out in a few seasons." I thought the flush cut looked cleaner, so I always went that route. He showed me on a older branch stub where the bark had died back and started peeling right where the flush cut was made. Since then I've been leaving a proper collar on every cut, even small ones, and the callus formation is way better. Has anyone else been taught the flush method and had to unlearn it, or is it just me? Maybe my old boss was just lazy and I picked up his bad habit.