One of the best shots i ever met shot compound w/o sights. he used a high anchor and sighted down the arrow.

Shooting a compound instinctivly is no different than shooting a recurve or longbow instinctivly. The principles are the same. Is it more difficult that using sites? Yes MUCH more difficult. It would require the same practice as would any other bow and you would also have to learn to adjust for string stretch moreso than with a longbow. That would require constant practise and keeping in tune with your bow. Sites are much easier to learn and much more productive in the field. Less likely to wound game with them if you stay in practise with sites and know your yardages.

I know a guy that shoots a compound without sites and have shot and hunted with him many times. He has been doing it for quite some time, and is remarkably good doing it. He can't quite get the groups that I do with a sight, but he does surprise me....

I saw Ted Nuget put some backstaps on the table without using sight's. But he get's to practice alot.