Enumeration Crystals are Base Raid Artifacts that increase the artifact production of a planet by 1. Though they are renewable resources, they are considered rare (depending on the legion you are in, the rate of bases per day, and their level) and opinions diverge on how to use them best.
Some consider that keeping them for a 15x+ planet is the best options, while others consider it "first come, first serve", using them on the best planet they have on hand. (Compare Long Term vs. Short Term strategies.) While some consider that the fact that they're Renewable resources means that using them as one would an Ability is more favorable to them, others consider that they're so rare that they should be treated as Non-renewable resources or at least semi-renewable and not being taken for granted, considering that perfecting a planet outweighs the short-term benefits of having a planet with a slightly higher artifact production.
Enumeration crystals can be used on planets that have no artifact production. The new designation will be "Extremely Sparse".