I wanted to make sure I didn't make this up in one of my senior moments, which can and does happen...; -} so I googled and found this. I've had a few comments on the subject and thought it would be worthwhile to post this information.
Consequences of Severe Pruning
Unfortunately, many homeowners and landscape professionals prune crape myrtle trees too severely. Topping--commonly called "crape murder"--can be very damaging and disfiguring to the tree. This practice results in a "witch's broom" appearance and a tree that is no longer in proportion.
Topping causes profuse growth at the site of the pruning, basal sprouting, and increases susceptibility to disease and insects. It encourages new growth that is too dense to allow air movement and light to reach the inner branches. Large "knobs" appear where trees have been trimmed repeatedly, and the topped tree has an unsightly appearance until new growth appears.
Although topping may result in larger blooms, those flowers will grow on thinner, weaker branches that will droop--especially after rain--and may even break. Topping may also shorten the life of your trees.
To properly prune crape myrtles, use the following techniques.
Remove suckers from the bottom of the plant.
Remove crossed, damaged, or diseased branches. For crossed branches, remove the weaker of the two limbs that are crossing or rubbing.
Prune the tips of the branches to remove old flowers. If old blooms are removed, a second blooming may occur.
Thin out small twiggy growth to allow air to better circulate in the canopy.