What does a speed sensor give?

I have a cheap cadence sensor (from aliexpress), and it works fine. I was thinking about buying another one as speed sensor, but then I thought: do I need it? I mean what does it give? The EE2 already knows my speed from the GPS. Or having both cadence and speed sensor connected would also enable some features I don't have now? (I have EE2, chest HR sensor, cadence sensor) Would it do some power calulations?

  • The speed sensor reacts quicker for speed than GPS does. It also might be more accurate (at times). So, if you are interested in personal speed records, a speed sensor might be better.

    It's also not that uncommon to lose GPS signal (the speed sensor will still work when that happens).

    No, having a speed sensor won't enable special power calculations.