Old Trash
Moving something to the Trash doesn’t free any space. It only goes away when the Trash is emptied, which many people rarely do.
What Roomy does
Items that have been in the Trash for more than 30 days are deleted for good during the daily tidy-up. Anything you trashed recently stays, so you still have time to change your mind.
Doing it without Roomy
macOS can do the same for the Trash on its own: in Finder, open Settings, choose Advanced, and turn on “Remove items from the Trash after 30 days”.