You have three types of objects
1.point entities ( player, info_targrt, sprites, etc... )
2. Brush Entities ( func_breakable, glass, door, etc.. (
3. Worldspawn which ID is 0, its not an entity.
Btw if any entity went outside of the sky/world a crash won't happen, you can tell when a player uses noclip and goes out of the map.
But if you spawn a point entity outside the world it might crash not sure.