In the lemon orchard event, what are the piles of leaves used for?

If you merge them to max level you can tap on them to get a chance of more leaves, energy orb, gears, or very rarely small gem.

IMO gems are very rare, I don't really use the gears (power up that speeds up recharge but a one time use), and sometimes it feels like you use more energy tapping the leaves vs the energy you MIGHT get back, so I usually sell the leaves once the board is clear of locked/grey items.