Yeah, it's simple but sometimes when sizing down, the jacket will spring back enough to cause it to separate from the core slightly. Not a problem with sizing small amounts or with 'soldered' jackets, but a definite consideration when sizing large differences or some standard-design jackets.

'Bumping up' OTOH tends to lock the jacket more firmly to the core, since the jacket will spring back slightly and the lead won't.
Regards, Joe

You can lead a man to logic but you can't make him think. NRA Life since 1976. God bless America!