You would generally blind bake in the instances where either the pie filling is unbaked (i.e., a mousse-type filling) or the moisture in the filling would cause the crust to become soggy before it bakes all the way through (i.e., custards or fruit fillings).
I always blind bake except in the case of a double-crust pie, where an uncooked top crust will not adhere to a cooked bottom crust. In these cases I will preheat a baking tray in the oven and place the pie on top to assist in thoroughly baking the bottom - also making sure I don't have too much liquid in the filling :-)
Hope this helps!
