It costs something to take away entities.
For example if I made a modded map and had none of those things there'd be a performance boost.
However, that's not the case with Altis as I know because the map is there, you can't edit it ( change mountains and etc. ) without modding it. But, you can hide objects and spawn them. But this is cost effective because it needs to hide that object every time the server starts up, etc. It may be beneficial FPS wise, but most likely not server side.
I'm basing this on information I've been told that using lots of triggers, hiding object functions, and other things to alter the map will cause more lag.
This ^ is why on my CQC when I had it I never touched map except for detecting if someone is outside their spawn.