A very popular view in academic philosophy is that knowledge of the history of philosophy is important for doing contemporary work in philosophy. But so much of the history of philosophy is filled with bad arguments and false theses, which serious people would never subscribe to.
How does painstaking familiarity with ancient mistakes and false propositions help us do philosophy today? It seems to me that false claims cannot ground anything -- or add anything valuable to what we know now. They are false!
I completely agree with the reasons Sean Greenberg gives for thinking that the history of philosophy is philosophically valuable, but I'm inclined to think that knowledge of philosophy's history is important for doing contemporary work, for exactly the reasons he offers. Knowledge of the history of philosophy helps contemporary philosophers to avoid re-inventing the wheel, with respect to both the questions we ask and the solutions we propose. More generally, I would add that, while false claims can't 'ground' anything, they can be extremely valuable as pointers towards more promising directions. The possibility of learning from one's mistakes shouldn't be underestimated!