You can compact the TimeSprite database by selecting File->Compact Database from the menu. This reorganizes the information in the database and releases unused space.
Normally free space in the database is reused, so the database should not need to be compacted regularly. The most obvious time you might want to do it is if you reduce the length of time that TimeSprite keeps data, which will reduce the amount of space needed.
The Compact function reports the amont of space freed.