ID:1658024
 
Keywords: dmm, dmp, maps
I'm not sure if there's any real advantage, disadvantage, or even difference. Is there any advantage to use .dmp maps over .dmm maps, or vice-versa, and if there is, why?
Sounds like not really if you don't have an issue.

http://www.byond.com/forum/?post=162143&hl=dmm%20vs%20dmp
There's no difference. The extension was changed years ago due to a naming conflict with some Windows dump file, which was also .dmp.