Rotom is probably the best spin blocker, has extremely defensive typing, ability and stats, and with the extra formes it gives it an extra niche to nail some specific pokemon down. (Leaf storm for swampert, overheat for scizor)
Rotom-H is the best counter for Scizor as it resists bullet punch, and threatens to hit first hard with overheat.
Upon switching Rotom into any unprepared attacker, it'll force the opposing party to switch out, therefore allowing you to scout more of the opponent's team.