To be more specific: every time a player enters a terrain with no other player in it, then there is a chance of creatures or bandits spawning.
There will be times when the terrain will be empty when you enter. That'll be rare, but it will happen. And creatures will now spawn in their correct terrain types, like Krayt Dragons in the Desert, and Space Slugs in Cave terrain.
Note that any player who's in a ship that's sitting in that terrain will prevent spawning, but one sitting above that terrain in atmo will not prevent spawning.