The more leaves a plant has the more likely it is to survive a catastrophe (other than mold/rot). Leaves do a lot of things, food reserves being one of them.
Also, there's no rule saying you can't harvest in stages. Take the top half when ripe and ready, leave the rest to finish up for a week or two.
Also, also, harvesting in stages can cause the plant to put out more trics in an attempt to save itself from the Creature chopping hunks o' plant away.