Its not only for SAMP
gtaIV SP & MP
I think i can answer why it's got disabled, its not synced.
You can check in SA SP. go to place where is grass and rocks take a screen go away from that place then come back and see if grass and rocks stays at the same place...
game just generates grass&rocks randomly on collision
If it wasn't disabled in MP it can cause some troubles
Examples:
1. player sees rock and stands on that rock, you see no rock at that place and it looks like he's standing in air (you will think mods or hacks)
2. player drives a car, drives on rock and jumps up with car, you dont see rock at that place and it will look like he's flying (you will think hacks)
3. you see rock in front of some player (player dosn't sees rock here he just drives a car) for you it will look like he's drives through rock (you will think it's some mod similar like lampost mod)
btw can you PM me that vehicle.txd hack, want to take a look into it
EDIT:
Searching info about grass in SAMP forum and yep i was right its got removed because of sync
http://forum.sa-mp.com/showthread.php?t=121150http://forum.sa-mp.com/showthread.php?t=100246now i hate how MP looks