The Progenitor is a new Origin coming to Stellaris Overlord Expansion, one which will require Utopia to be available for playing. Looking at its description, we can see why it's part of the Overlord.
The hive relies heavily on the presence of powerful Offspring. While they are near, the hive thrives and functions with great efficiency.
Offspring Vessels can be included in your fleets, providing an aura that cancels out the inherent penalties of your ships, providing a net small bonus. You are limited in the number of Offspring Vessels your empire can support at any given time, based on your overall naval capacity, similar to the Titan limit.
In turn, the Offspring Vessels share a pool, with larger ships taking a greater portion of the pool.
Additionally, there is also a starbase building to protect your empire space, which provides greater benefits than the ships. The Offspring Nest itself, replaces the Spawning Pools of regular hives, providing additional bonuses. It's likely that you will want one of these on each of your planets.
Unlike other hives, the Progenitor is able to release sectors as vassals, placing the fate of the sector in the tendrils of an Offspring which is promoted to Progenitor status and becomes the ruler of the new empire. Progenitor subjects released inherit the Progenitor Hive origin from your empire, with all the bonuses and penalties that it entails.
Should you have a subject that is not a Progenitor Hive, you can build an Offspring Nest on their world, providing some much-needed oversight to their drones. Or workers, if you want to be civil.