/clearvehicles
- Removes all existing vehicles.
/clearspambricks
- Clears all the useless vehicle spawns and spam not on a baseplate.
/clearfarawaybricks
- Clears all the useless vehicle spawns and spam you cannot currently see. (within about 2000 horizontal studs)
By clearing all the vehicles you remove all lag that they cause.
By clearing all bricks not on a baseplate you remove all the useless item or vehicle spawns people have placed.
By clearing 'far away' bricks you can remove any spam you cannot see.
If people persist in re-making vehicles when you don't want them, ban them or enable something like Server Build Trust.