I hope you don't mind if I add emphasis to this subtly stated but very
important point of Gerald's. The slope on the Phillips and flat bladed
screwdrivers constitutes a "weak link" which serves to reduce the likelihood
of snapping or through-driving screws due to overtorquing (by creating
slippage between the screw head and the bit), particularly when using a
power driver. My cordless drill-driver, as do most air drivers I have seen,
has an adjustable torque clutch which serves the same purpose very
effectively, without stripping heads/slots.
Robertson and torx bits combined with a power driver need to be used
carefully for this reason.
As miserable as stripped screw heads are, so are snapped screws and
damaged walnut or mahogany panels.