yes the point is to develop sets for different tanking challanges.
The EH set is mainly for progression - giving your healers as much room to play with as possible.
Block Value - tanking trash
Aggro - specific fights have higher or lower threat requirements - dont under or overthreat. This requires experience and depends on the raid healers & dps.
Avoidance - when you want to give your healers a break - and the risk of being smushed into a greasy stain on the floor is low.
4 piece T8 - any boss with a predictable magical burst
Mix and Match - yes absolutely. Play with your trinkets, set pieces etc.