Warren Huart breaks down why reverbs and delays need their own EQ, since they exaggerate whatever frequencies feed into them. A kick drum with excess low end turns into a boomy wash once reverb picks it up, so high-passing the return keeps the hit defined instead of muddy.
The same logic applies to cymbals. Bleed in the 5 to 7kHz range gets amplified by reverb, so Warren often runs a de-esser before the send to duck that harshness before it ever hits the effect.
He also shares the classic trick of stripping both low and high end from a vocal or snare before it hits reverb, giving you ambience without exaggerating sibilance or cymbal wash.
Placing EQ before the reverb or delay, rather than after, tames the effect without strangling it, and lets you shape brightness per instrument instead of using one blanket treatment.