I seem to recall some saying that a scope should be mounted as low to the barrel as possible/practical on a benchrest rifle. ? Pros - Cons, Whys - Wherefores ?
Thanks.

it also helps keep your cheek down on the stock.

I don't think so. Parallax with a certain scope and setting and range is independent of scope height; or/and of whether the scope is mounted on a rifle or not. 
And elevation change is independent of scope height. 

Scope height is only about comfort, as long as there's no scope/gun interference. 


"The closer the scope is to the rifle's bore, the less parallax effect. The point the crosshairs and the bullet's path intersect is less affected the closer the two parallel lines are to each other. So as you take shots further out it requires less elevation change. "
Here's a good explanation:

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My mistake. Parallax is the wrong terminology to describe the point where scope and bullet's path intersect. And I honestly don't recall the terminology for this intersection.
But the closer the scope is to the bore, the less change there is between that point where they intersect as you shots move before or after the point they intersect. 
So having the scope very high above the bore will mean the point the crosshairs and bullet's path intersect will be a steeper angle at a closer distance. As you move out further the angle between the bore and scope becomes less acute. So at very long distances the distance between bore and scope centerlines wont have as much affect on the angle they intersect at.

Most target shooters who use scoped rifles for varying distances keep a cheat sheet taped to their stocks to indicate scope settings for various distances, so they know how many clicks equals a certain number of inches of elevation at each distance. The number of clicks per inch or foot changes as the intersecting point gets further out and angles decrease.