Ask Mr. Smarty Plants

It depends.  You didn’t say what kind of mature trees you have.

If the trees are Oaks - - Then the answer is “Not Now!” .  The link here is to an earlier Mr Smarty Plants question and references which give you a good overview of the dangers of Oak Wilt and how you can attempt to protect your trees.  The short version of this is to prune only in the “depth” of the cold winter, preferably January & February.

Looking farther afield, I found two good and local articles on why you could want to prune a tree.  The short version of their advice is  “ health, cosmetics & safety”.  The first of these is an article from the city of Round Rock on Pruning Mature Trees, which discusses reasons for pruning.  Their basic philosophy is that “Pruning is the most common, yet often unnecessary, tree maintenance procedure.”    Trees should be pruned for three reasons “safety, health, and aesthetics”.   Very similar advice is given in a blog from the Austin Tree Experts on “Why to Prune Trees in Austin TX”.

So, how does this affect your perception of the mature trees?  Assuming they are not Oaks, then an argument could be made that the trunk growth is not very good looking, or that in due time, branches growing there would be unsafe. [I consistently get a scratch on my head from the low branches of our plum tree while mowing!]  Its not necessary to prune your trees, but if you wish, this is the justification.   Mr Smarty Plants does have a good answer on pruning Chinkapin oak, Loquat and Monterrey oak trees. 

Similarly, to help you do it right, the Wildflower Center has a Step by Step Guide on How to Prune a Tree.