Bob,
I see these on courses that have been lengthened, because a lot of times there isn't enough room in the straight back direction to lengthen the hole. My home course has a great example of this on #9, when it was lengthened from 426 yards to 449. That tee is about 40 yards right and 15 feet lower than than old tee, so it plays totally differently from over there despite only adding 23 yards to the scorecard total.
I saw a lot of this on a course I played most recently last fall in Missouri, the name of which is on the tip of my tongue but I can't spit it out at the moment. It had a bunch of new tees added to bring its length up to 7510 yards, and it plays totally differently from back there more from the odd angles you get than the extra few hundred yards. I don't really have the skill to work the ball on demand with my driver and it wasn't a problem before on the old tees, but on those new back tees there are several holes where that really becomes a liability requiring a much more precise shot than would otherwise be the case. Because of the extreme hilliness of the terrain, there are plenty of places where the fairway is on a ridge with ravines of death down both sides, and the more angle you can work you ball the wider and/or deeper you can make your target area.