I agree completely with Geoffrey...variety is key.
Using Merion, or even Cobb's Creek (shameless restoration promotion) for an example, the key is that the long holes are very long (and usually uphill), the short holes are very short (and often downhill), there is at least one very short par three, there is a paucity of par fives, and greensites are elevated and intensely demanding while positioning the ball to the proper place in the fairway is way more important than length.
It's called thoughtful, integrated design, and it seems that on most modern course, multiple tees (and cart paths) facilitate a different type of disjointed thinking.
The funny thing is that most of these back tees will be played a handful of times.