Perhaps the most space consuming items in the ProcessRobot database are the Processes themselves. Processes saved in the database contain everything - actions, selectors, image controls etc.
It is important to know that simply saving a Process only overwrites the previous, most recent version; saving and committing, however, saves the current version as a standalone, permanently stored version in the database. Whenever needed, this version can be reloaded from the database using the History button in the Process Studio.
Keeping a lot of committed versions, however, requires a lot of database space. Should you wish to reduce the amount of used database space, it might be a good idea to remove past versions of Processes which are already tested and functioning properly. In order to do so, you may open the History of a Process in Process Studio and right-click on the version you wish to keep - afterwards, select "Save as new Process", and delete the original one. This will only leave the newly saved version, which will be independent from the old one, and will have a clear history; this will free the space where all the past committed versions were stored.