There are seals that are balanced with both cost and slot space e.g. you could get similar stat up from two slots and spread costs, or one slot. It's like how seals cost 0, but they still take slots. There are also seals that change your reward depending on how many spare points you got.
Slots stay consistent (there are going to be upgrades in future), but how many points of power you get depends on what seals you use.
The mechanic is you need to use some negative seals to be able to use positive ones, but you also must think of the slots. There are seals that cost a lot, and gaining points from multiple smaller neg seals may not be enough. If you want something real good, you may need to use something real bad instead of many minorly bad seals. Of course there are different synergies, and sometimes the bad ones can became not so bad, so there is extra layer of balancing to that.