This mod adds some flavor to pirates. It's easy to completely ignore them, specially in the late game, when they are no more than a nuisance. They are pretty inconsequential.
Now, if a system with pirates stays unnatended for too long (10 years or more), the pirates will try to seize a nearby colony. If they win, they will become an independent megacorp with the Criminal Heritage civic!
There's more: the newly-formed "Pirate Republic" may offer to become your tributary in exchange of the system. This offer will only appear if you do not already have another rebelious pirate as a vassal.
This mod was inspired by this suggestion published on the official Stellaris forums.