Benefits for me:
1). Time saver/multitasker. I can mow, sleep, work, cook, drink, etc while the robot cleans the pool.
2). Super clean water. If I throw the robot into my pool when its "clean", the filter bag will still make a cloudy mess of the 5 gallon rinse bucket at the end of the cycle.
3). Completeness of job. I get tired, bored, rushed, etc and miss spots with the vacuum. The robot doesn't. He lives to clean the pool

Are you missing out on any great zen experience by not having one? No. Are you saving some money by not having one? Yes.
Would I buy another one? Absolutely!