By far, the biggest use of philosophy, that probably isn't even mentioned by anyone, is that you inherit millenia of thought that came before you.

Without philosophy, you're relying on your local culture -- which probably hasn't incorporated all of the accomplishments that have occurred since the beginning of Time.

The other reason is to hone your use of dialectic and reason. These are perhaps the only tools you have to survive the onslaught of the opinions and pressure of the masses to conform or agree. If we were in a healthy society, this wouldn't be so necessary, but we are surrounded by pressures and hostilities of reason on a daily basis -- things which will affect us within our lifetimes.

Don't be one of "them".