In principle, anyone can use this strategy to determine which of the two specialized schools to develop. Of course, it is much more effective for mages, as they will have high-level spells not only from the specialized schools. Therefore, I don't use it for other factions, and I haven't played as mages yet. And I'm not even sure if I will. However, for warlocks, I try to build a Guild of level 3 as quickly as possible to determine which ability to take in Chaos (I always take it): Fire Lord, Storm Lord, or Life Lord. My main opponent in HotS is a mage. Therefore, I try to take Mana Burst.