In the world I live in (production machine shop), we would sometimes part off in reverse for the simple reason the part would not try to lift off and hit us. Instead it sends it down into the chip tub of the machine.
For the most part we don't do that anymore. NCs have taken over... btw, some of them run in reverse all the time.
Another time to run in reverse... if you are making lots of small chips and they are coming out and making a mess... well, if you run in reverse with the tool upside down... all the chips go straight down - much cleaner in the shop. Obviously you cannot make heavy cuts or have a screw on chuck like I have on my machine.
This discussion brings back memories... been a long time since I started in the trade.
FWIW: I have worked with some very impressive machinists and tool and die makers... You guys, on this forum, don't have to take your hats off to anyone...
Thm: