Right above every leaf on the plant is a tiny bud. These little buds are called axillary meristems. At the top of the plant, the main growth point is the apical meristem. The apical meristem helps balance the plant hormones that keep the axillary meristems in check. When the plant is topped and the apical meristem is removed the axillary meristems kick in and start forming suckers. Stress can induce this as well and some varieties are just more likely to sucker even if the apical meristem is present.
If you are seeing what looks like two or three leaves starting above a regular leaf like in
@Knucklehead pics earlier in this post you can just carefully pinch these off. In the very center of the little leaf cluster is the axillary meristem that is responsible for the growth of the sucker. A few small suckers here and there probably don't make a huge difference but some of them really take off in a hurry.