There’s lots of good reasons to prune bushes, shrubs, trees, and even flowers. We cut off diseased parts and those parts that are likely to get diseased (such a rubbing branches), cut to rejuvenate a plant (when you want to force it to make new growth), make it grow where you want it to grow (such as opening a fruit tree up on the inside to get more light to the center), and strengthen it (such as cutting off a double leader or weak crotch on a tree).
An embarrassing reason to prune is because we have planted a plant that are too large for its location and it has to be made smaller. But at least we can correct the situation by pruning.
We also prune for pure beauty, such as pruning a hedge, or espaliering a fruit tree against a wall, or making a topiary of a bush.
But why southern gardeners feel it necessary to decapitate their crepe myrtles we’ll never understand!
These are gentle beauties, People! They don’t bite back!
They might develop multiple trunks, and if you don’t like that, you can cut back to the number of trunks you want to see thrive, but don’t just butcher these gentle plants (or commit crepe murder as some have said because you can)!
Go out now and let a new trunk or two sprout up and restrain yourself from cutting it. When a few new trunks have formed, then cut down the ugliness you have created and let the rejuvenated tree smile in the sun!