It depends on the area, how much water is there, what kind of elk you are after, and many other factors. I hate sitting, I put on 170 miles in Sept hunting elk, I passed up a lot of bulls, killed a nice bull ambushing him and could have easily killed many more after my tag was filled. Being where elk are is the key, if we bed a bull/herd in an area too thick to stalk we get our wind right and sit, sometimes we sit a close by wallow, sometimes we sit a feeding feature. Once the elk start moving/talking we try to get to where they are going before them.
We don't just sit random places though, learn the area, spots elk frequent and then decide if you want to sit or move. Personally I hate sitting for very long and only do it when absolutely necessary. I have a tree stand I put up on a water hole that has big bulls hitting it on most days throughout Sept. I've sat that stand maybe 5 hours in the last 10 years, I know I would be successful sitting it but just don't want to fill my tag sitting in a tree.
Well used water is probably the best bet for elk, however make sure it's well used, just because a wallow is dirty when you get to it doesn't mean it will be hit again any time soon. One of the areas we hunted this year had probably 25 wallows in the basin, one wallow was getting hit pretty regular but all of them were active.
A few years back we were chasing a giant 360+ bull on a OIL hunt, we hunted that bull for close to a week and he was running a bench back and forth and we could never get caught up with him and in range. Finally we decided to just go sit along the elk trail on the bench and wait for him to come up. We were sitting there for about 30 minutes and he came up and bedded 100 yards away, I was able to crawl close enough for a 60 yard shot and hit a small branch that deflected my arrow. That is about the only time I can think of where sitting paid off, the main reason being that we knew exactly where he kept ending up.
Rifle hunting IMO is different, if you can sit somewhere where you can see out to your effective range and be patient then sitting can work very well in good elk country. WIth a bow you need to be able to sit within 50 yards of where the elk will be and that's a lot to ask while still trying to play the wind.