Lightweight comfort and stability with overall cushioning and flexibility, but without all the added cushioning in the heel - making them into what Pirie called an 'orthopaedic boot'.
My usual training shoes - New Balance RX Terrains - have virtually no cushioning at all but are only worn for running on the fells, fields and riverbanks - which is where most of my training is done. Except when racing I avoid tarmac like the plague!
For trail racing and mixed terrain training I wear New Balance 781's that have just the right amount of cushioning to protect my feet from uneven rough or stony ground. I'll probably wear the latter for my next 10K road race too.