A gank does not always have to end in a kill
Even just showing your face is sometimes enough to give us an advantage. Sure we might be pushed out from being directly under our tower, you can still gank. Every lane has many ways from where to enter it. Get creative, maybe gank from behind their own tower and knock them forward or something. But don't just afk farm the entire match because it is a better use of your time according to you. Even Yi, a champion famous for the "AFK farm till 6" routine, has pressure if he shows in a lane before hand. if suddenly the bot lane has 3 champions on a team, usually the other side backs off or changes their play style. Sometimes just making them miss a few CS is enough to take a solid lead. Just because you may not get a kill, does not mean it is not worth ganking the lane.