I think the only issue is on some things, rewards can undermine intrinsic motivation... external rewards work for tasks where extrinsic motivation works well
I think this mainly comes down to how good you are at systematic thinking. For example it's really hard to build a habit without some form of reward mechanism, but once that habit is built the reward comes from the consistency of keeping the habit. This type of reward oriented behavior is probably quite good for that initial difficulty most people have in building a habit, but once you have the system in place it becomes second nature to keep doing the task and as a consequence usually introduces some negative association with skipping it. Think the gym for example.
