Plants possess a modular genetic blueprint where unexpressed pathways act like latent slots waiting for environmental triggers or evolutionary changes.
Not useless, think of them like un-used genetic appendage slots, some plants utilize them some do not.
Similar to when you are loading equipment on your mechs/vehichle in video games, depending on what tools/weapons you use, some slots are used some are not. Its all a very complex blend of tailored genetical expression across time. I like to think of it, to simplify it is think of it like equipment "slot(empty)"