Is it possible that setting up BPS PRO might have an impact on mysql data base size?
Regulary it had about 9mb compressed but after setting all BPS PRO settings and getting rid off Wordfence and website Defender suddenly my database table is 6,5mb compressed.
If you delete/remove plugins that are storing data in your database then yes your MySQL database size should go down/decrease because you would be removing/deleting data from database tables in your Database.