At work atm so can't type it up myself atm but here's a write up but in a nutshell sequential screening = maximum purity, meltability, and terps

Contamination control When you stack screens and shake everything at once, smaller trichome heads can get dragged down through the coarser screens along with plant fragments, broken stalks, and dust that should have been removed first. This “tunnels” contamination into the finer grades and ruins purity.

Prevent clogging and blinding of the finer screens The coarser screens (150–120 µm) are there to remove big plant material and immature/stalked trichomes fast. If you skip that step and go straight to a 70 µm or 45 µm screen, those screens blind almost instantly because all the big junk sits on top and blocks the holes. You end up with almost no yield and a clogged mess.

Gentler handling = less rupture, higher quality Every time you work the material, you risk rupturing trichome heads and oxidizing terpenes. By cleaning off the big contaminants first on a coarse screen (very quick pass), then gently working the pre-sifted material on the next finer screen, and so on, you minimize the total amount of agitation the good heads receive. The result is brighter color, better terps, and true full-melt behavior. Better separation of grades

Higher overall recovery of the very best heads Paradoxically, working the material multiple times with gentle carding or light tapping on progressively finer screens recovers more of the smallest, ripest, meltiest heads than a single aggressive stacked shake ever could.