The idea behind LPC is that proteine ( meat, fish , soy ) is not always easely available.
Isolating proteine from plant leaves is a reasonable simple way to improve peoples diet.
Practical: LPC is produced by pulping leaves and pressing the juice out, heating the juice to coagulate the protein, and filtering the protein out and drying it.(Wikipedia)
PLC is also a proteine source for animals reducing puchased foods.
A drawback is its possible strong offtaste.
The most interresting leafplants i.m.o. are chards, sweet potato leaves and allium spp. leaves.
Purification is not that easy ,or at least too my knowledge.