Whenever an empty map is opened it increases the file size drastically. From my experience, 4 new opened maps adds 1 megabyte of data to the world file, and there is no way of getting rid those megabytes. This makes it scary making large map rooms, due to irreversible, large file size. 

Steps to reproduce: 
1. Make a new world, then leave it.
2. Check the world size, then rejoin. 
3. Open 3-4 new empty maps.
4. Leave the world and see the world size have increased.