Robots can be assigned to Oil Rigs to harvest $OIL. Harvesting Skill and Stats (mainly STR) of the Robot will determine the amount of $OIL the Robot can harvest. Different Oil Rigs have different Elements, matching a Robot with the right Element will increase its performance.
Having Liquidity in the same pool (Oil Rig) as your Robot might allow it to boost your Liquidity Mining APY (by increasing your weight in the pool) and increase the percentage of the mined rewards that will be unlocked.
Ultra-rare Items can also come out of Harvesting Quests in addition to $OIL. For example, Resurrection Stones of Epic Rarity and higher can only be found on Harvesting quests.