I heve about nine. Many are about 14 feet tall and I usually cut them back to about 6 feet. I like them large and bushy and they always produce plenty of flowers. I,m not an expert on this matter however. In my neighborhood we had some fairly decent sized bushes that were cut back to about a foot and after three years they are still struggling to grow back. I add fertilizer and give them water when it's extra hot and they are gorgeous.

Mine doesn't lose it's leaves, but I cut it way back every spring anyway. Mine is planted in a place where I have to have some control of it---cutting it back every year so it has to start over is the only way to do that.
If you are lucky, and yours a growing in an open space, just let them grow. They will do fine either way.

Wish I'd cut mine back last fall - the January winds knocked it over. I pulled it back upright and tied it to a couple of stakes, then a February wind came along and knocked it over in a different direction... half of it is now dead and I'm afraid the rest will go when I try to straighten it out again.

If you don't have wind or hard freezes to worry about, you don't have to cut it back. Around here (Mendocino) there are lots of really tall ones that never get cut back.