There were arguments some time ago against Northern being allowed to introduce advance tickets on a number of services as these would bring passengers off the express services onto local trains where space was a problem. That said, there was a general acceptance that a lower quality, slower route should certainly be offered at a lower cost.
I'm of the view where there is capacity on slower, lower quality trains there should be a routing available for that service, but I believe that long term, 70% of UK advance ticket flows (ie all the pointless, short journey, post-2010 ones) and 90% of the TOC-only routing tickets in this country need removing.