Yes. Farming is one of the most, if not the most, critical part of the game. Carries that can not die and get a large quantity of the available farm will shred champions late game. If you play a role that's not support or jungler it is crucial to pay attention to your early game last hits. Later in the game if you are repositioning yourself on the map but haven't actually made any engagements with the enemy team in the last minute you must ask yourself if you should be farming instead. Farming is important at all stages of the game with two exceptions: You're full build. You believe you can win a team fights and have a way to initiate one.