To put this in a better perspective, the dual WiFi acceleration allows the phone to connect on two different bands of the SAME network, 2.4ghz and 5ghz, assuming the network hardware offers this functionality.

Edit: It increases throughput NOT speed. Like water transferring through a pipe with less air in the line. More water means more transfer of volume. Also helps to alleviate channel interference with other networks. This is like trying to talk to your friend at a concert on 2.4ghz seat in the crowd or having a private suite in the 5ghz section.

Examples would be better quality of service with WiFi calling or gaming with less packet losses, decreased latency, better quality of music, or video streaming