Contrary to popular belief cutting back or trimming a palm tree does not aide the palm tree in growing faster. Depending on how much and how often it could actually have the opposite effect. Pruning a palm tree like most other plants should be done carefully.
The main reason for trimming palms trees is to remove broken, dead or dying fronds. By doing this you help protect the tree from damaging itself and also stifling growth. Another reason is that the dead debris provides a nesting place for rats and other unwanted pests.
In addition to the previous reason for trimming back palm trees would be for the well being of property and anyone who maybe be walking by if one of the heavy branches were to fall. Unlike other trees palm trees have a cycle of growth where eventually the large palms die off and shed to allow new growth. Even when dried out these branches can still be dangerous because of their size, weight and thorns that are associated with it.