Ask Mr. Smarty Plants

Yucca filamentosa (Adam's needle) doesn't need pruning per se. You should always cut back the woody blooms stalk as soon as blooming is over unless you are planning to harvest seeds. If you are trying to harvest seeds, the chartreuse-green seed pods should remain on the plant until they turn brown or black and begin to split. This article from Ohio State University on Yucca filamentosa  will give you some information on trimming the basal foliage. If some of your yuccas are beginning to outgrow the area in which you want them to grow, you might do some trimming on the blades that are protruding where you don't want them.  Please be very careful, protecting yourself or whoever is doing the trimming. Heavy clothing covering and protecting the arms and legs, leather gloves and even goggles are all necessary. As you bend over to trim the trunk, those sharp points are going to be trying to get you wherever they can. You especially don't want one of those in your eye. To quote from that article:

"Dead basal foliage needs to be carefully removed with a sharp knife in early Spring (wear gloves; the tough foliage can be sharp on its edges, in addition to the knife), and immature fruiting stalks are best pruned away just after flowering has finished in mid-Summer."

Pictures of Yucca filamentosa