There isn’t really a hard rule for how frequently you should do it - its entirely dependent upon how frequently assets are deleted on your instance. That said, you should consider it in conjunction with your backup strategy, if you’re backing up weekly but compacting daily some blobs may never make into your backups. Only you can decide whether this is an issue or not.
On a large instance it may take time to run if you haven’t previously so you may want to consider scheduling it for a quiet time (perhaps on a weekend?)