I am all about the hoarding of recruits, finished extra low cost heroes, and ascension materials once you have a decent 4* 4.70 rainbow team, and two decent 4* 3.60 rainbow teams ( total of three heroes of each color, total of fifteen heroes ).
A 4* 4.70 takes 47% the XP of a 5* 4.80 and half the 3* ascension materials. Which is good for resources, a deep bench, Rare Ascension Item Quests and Challenge events.
But any nonfarmable ascension material you use on 4* heroes will not be recoverable for 5* heroes. Any 4* 4.70 hero use to level a later 5* hero loses 90% of the XP invested in it. Or 42.3% of the XP needed to level a 5* 4.80 hero.
Later, creating one 5* 4.80 rainbow team and two 5* 3.70 rainbow teams will take the same 3* ascension items as four rainbow 4* 4.70 teams.
In fact I am more tempted to hoard until the final four 4* heroes are revealed ( reflect red and reflect green events ) and the Devs strategy for past HotM is revealed.