The main reason for the change in rules is to speed up play. I totally agree and feel that leaving the flagstick in the hole on long putts makes sense and should be done
Shorter putts become much more personal. I know several tour players such as Bryson DeChambeau and Adam Scott leave the flag in all the time.
My son Brien was a teammate of Adams and a much better putter. His control of distance was similar to Ben Crenshaw. His comment was “if I hit the putt at perfect speed, how can the flag help?” I agree and will usually take the flag out under 15-20 feet.