What are MTRs used for? Ok, before you say, "Military Training Routes are used for... uhh... military training," let me elaborate.

I've read about how they work with ATC and speed restrictions etc. What I'm wondering is what they do on them. 

Take, for instance, IR-504. It starts in the middle of nowhere about 20 miles south of the BUM vortac in western Missouri, almost 70 miles from the nearest Air Force Base. It takes numerous turns and meanders, seemingly randomly all over northeastern Kansas. It finally ends in an MOA in the middle of the state, but once again, not by a base or anything. 

I can't see any rhyme or reason to the routing and can't imagine what it would be used to train for. It's not bombing practice; only a very small section is inside an MOA. It can't be terrain following exercises; its an IFR route and 3 digits means over 1500ft agl. Besides, what terrain could they be following? We're talking about central Kansas here.

What in the world do they use these routes for?
There is a description of this route page 1-139 of "Area Planning, MTR". 

  

The scan is not good, you may get the textual content here too.

It says terrain following activities may take place, as well as visual contours (which I assume to be navigating without radar, looking at the outdoor and searching in a catalog the same relief contour to know where you are). As you commented, taking into account the local relief:


For terrain following should be for newbies.
For visual contours navigation should be for top-guns only.


There are different routes like this, starting from nowhere and ending in the Smoky MOA. They seem to be routes avoiding nearby airfields. On the image below, I've emphasized the area without airfields, including MOAs. It looks like IR-504 is drawn along the centerline.


Based on VFRMAP

Other possible selection criteria:


Unpopulated areas (noise from low flying jets)
Low radio noise areas.
Flat terrain for UAV training.