For power delivery we read the power 4 times per second from your power meter or smart trainer. Power delivery affects the value that is sent to the server for calculations.

With instant power delivery we send the instantaneous value.
With 1s AVG we do an average over the last 0.5 - 1 seconds. This is to ensure there are no sudden spikes in power and also helps users which experience occasional signal interference to avoid getting 0 power which would affect their speed and make for an unpleasant experience.
With 3s AVG we do an average over the 0.5 - 3 seconds. This setting is again to ensure there are no sudden spikes in power and also helps users that experience more frequent power spikes.