I agree with La Puce as I've read a lot on this having had the same
questions.

Even Mr Titchmarsh recommends only cutting back some of the branches
and leaving the others.

Pruning hard back gives max WINTER stems but will obviously not give
you much in the way of anything while it is growing for the rest of the
year.

Some books , websites etc say to prun hard back but then don't say how
often. some as Mr T say go the half way house and only some of the
branches.

Of course you can also take cuttings to start growing more and then
when your new ones are growing the olds ones can be pruned hard etc .
All depends on if you want all year value of max value in winter.

Anyway I'm no expert this is just what I've read etc from elsewhere