All plants whether trees shrubs evergreen or even annuals & perennials can be made more productive by pruning.
Example – when buying petunias, if you remove all buds & this means to pinch them off & pinch all growing ends back to the closest set of leaves, where you first had one branch of flowers now you will have double the amount. Pinching or pruning causes the plants to stop growing straight up & put out side shoots. Sometimes you will notice hanging baskets of Fuchsia that are very spindly & other baskets that are very full of growth & flowers, it is because someone took the time early in the season & pinched that basket of flowers several times to cause fullness.
Rule of thumb for pruning flowering shrubs, if the shrub flowers early spring, prune(cut off ends) immediately after flowering, Forsythia is a prime example. If a shrub blooms mid summer or early fall prune only very early spring. This group blooms on new wood.
NEVER prune or fertilize after the end of July. Both these practices will cause new growth that will not harden off before frost comes and the new growth can freeze off.
Cutting back deadwood is OK in spring but be careful, previous years growth holds your new flowers for spring.
Old flower heads should have been cut back immediately after flowering on early spring & early summer flowering shrubs. This is a good practice with annuals & perennials as many times perennials will come back into flower if they aren’t allowed to go to seed and annuals like petunias & especially pansies will stop flowering if allowed to go to seed.