While they're not dormant, they're not exactly exerting themselves. Generally, they're conserving energy for the next growth spurt in the fall. This resting time is a great opportunity for humans to get off the lawn chair, rummage around in the shed for clippers, and do some light pruning.
In the spring, trees can send out long sprays of growth that make the outline of the tree look weird. Clipping these sprays back by one half to two thirds can rein in the tree and recapture its glory.
When the fall growth spurt happens the tree will look much more balanced!