Yews as a green footer are nice enough but they can become overbearing. The owner of this hedge asked, "Can I cut my yews down again? They've gotten so woody it's hard to shear them."
She can discuss this without trepidation because she's seen them make a comeback once already.
At left (preceding picture) is the hedge in the fall, a little more than five years ago.
And at right (next image) is the hedge the following April.
However, the inward slope we'd given the hedge -- top narrower than foot -- gradually changed. By year four, an outward slope had developed. It was not yet a severe slope but it was enough that the upper branches began shading the lower.
So here we are this spring, back to raw wood once more. On the left, simply sheared. On the right, after being thinned.
See how densely clustered the stub ends are? Of course those were hard to shear. When we thin those stubs there will be new, softer growth coming from all over the interior to fill that space.
Thinning is essential for the shrub's health, too. New growth comes primarily from the top of a stub. If the hedge remained as you see it at left (preceding image), the stub-end shoots would create such a dense mat that all interior growth would be shaded out.
All that wood needs energy; only leaves can make energy. When a plant's scale tips toward more wood than leaf, it becomes weaker.
After thinning, there are stubs from the depths to the top, so the hedge will have more leaves -- more energy -- than ever.