What philosophy of mathematics is about

Found via a reference at the M-Phi blog, here a pretty clear statement on what the philosophy of mathematics is all about:

• A Guide for the Perplexed: What Mathematicians Need to Know to Understand Philosophers of Mathematics (Mark Balaguer)

This does, indeed, seem to capture much of what philosophers of mathematics are studying.  However, it fails to persuade me that such study is useful to mathematicians.