For example.
Centaurs: Good against mass frontline, especially swift or arcane armor.
Four Eyes: Good against units with large health pools of any armor type, especially those with 4k+
I just lost a game because a Diamond player sent Four Eyes and Centaurs against Hades spam due to a few Hydras.
The Centaur send was okay~ due to other units, but the Four Eyes straight up cost us the game.
When I brought this up to the player in question, he thought he was making the right call due to there being hydras as well.
He thought Four Eyes was a good send against Hydras.
After informing him that he would have been better served with Needlers to counter the Hades/other units, he thanked me and said he'd remember it.
Obviously this player is responsive to guidance and that's all they needed.
The fact that he made it to diamond without getting that guidance is shameful though. Thus my suggestion.