You are presuming a value function -- utility -- for the very subject that questions values, presumptions and what it even means to know. You have to take a step back :)

As logic is the foundation of mathematics even though very little mathematicians directly care about those foundations -- and you certainly don't need to fully understand them in order to understand almost all math -- so too is philosophy the foundation of knowledge and value. You don't need to understand it in order to do science, but it is a foundation nonetheless. It is best, therefore, not to ask questions like "what is it good for/how is it useful" before venturing into philosophy, because philosophy grapples precisely with questions like "is utility good?" and "what is good anyway?" You study philosophy because you wish to ponder the foundations to everything. Either those questions will resolve themselves for you or they won't...