You can set a database with an intial size. This is preferred if you have an estimated size your database needs to be than to having a very small data file that has to issue a lot of growth events which can lead to bad fragmentation. The space that is not used is white space in the file that is reserved for future use.

TempDB get objects created and dropped all the time depending on the operations that are going on with different databases. The thing you want to watch out for is to ensure that TempDB does not fill up where it cannot grow if necessary.