Cutting back shrubs keeps precious plants healthy ... ‘Over the course of three years you have reduced the shrub but doing it this way it will still carry on flowering every year.
The best way to rejuvenate these plants is to cut them back during the dormant season. First cut out dead, diseased and crossing stems, and then thin the number of remaining stems by half.
Foraging a few stems from flowering trees and shrubs is a wonderful way to bring spring indoors ... it might be to “harvest” generously, when cutting branches be sensitive to the plant ...