Triggers autophagy and dark-induced senescence. Extended dark triggers programmed cell death or PCD, Protein/enzyme synthesis is upregulated, accelerating breakdown of chlorypyl among other things. Just be grateful to make it to harvest. Enzymes drastically lower the activation energy required for chemical reactions. They function similarly to coefficient multipliers, exponentially increasing the reaction rate, not just x1,2,3, talking anywhere up to 10^{17}.
Understand that when you cut a stem off to harvest, the stem, similar to a clone cutting, is not clinically dead; it hasn't triggered biological PCD, stem/enters a highly active transition phase where it balances Programmed Cell Death (PCD), and cellular regeneration. Until water levels force its hand, by then it's been 3 days @ 60/60, plant is almost dry, and it's not even begun to breakdown chlorphyl its spent 3 days in regenerative mode, 0 Enzyme release. Sorta how it works. For cell death to be classified as PCD, the cell must remain metabolically active enough to execute its own genetically controlled self-destruction sequence. Can't just hack it off or boil the roots. That's necrosis.
One tries to signal the trigger, PCD upregulates the enzyme, then harvest. If you just hack it off, it spends days "hanging", "drying" in "regenerative" mode before PCD is signaled and triggered.