If you grow asters your will know that sometimes they are tall and skinny and prone to falling over. And their lower leaves are often lost to mildew, leaving the base of their stems looking kind of awful. You can improve their situation by pinching them, that is, taking out the uppermost couple of sets of leaves once in early June, and then again the beginning of July. If you do this, the plant will be slightly shorter and stalkier than it would have been otherwise. You have nipped off the top growth so they bush out horizontally.
You can do the whole plant, or the part at the front, leaving the stems towards the back to be a bit taller, or just every other tip. Try different things. And you can do this with other plants as well, although phlox is the only really suitable other one I can think of right now...( maybe I’ll come up with some others by morning...)
On the BBC show, Gardeners' World, they call it the Chelsea Chop. People who tend the plants at the famous Chelsea Flower Show take pruning shears to asters and phlox to make them lush and bushy. They have a longer season to produce bloom, and many more plants to deal with, so I would stick with pinching, if I could choose. It just feels better to pinch than to chop!
Aster leaf on left, not pinched. Aster leaves on the right, pinched from top. They will produce side growth.