ASIO driver decreases the audio latency on Windows operating system.
The latency is the delay between the demand of the sound, and the effective sound rendering. To be "playable", you must have a latency less than 30 ms (including inputs / outputs of the software and the Operating System).
It exists an universal Asio driver for PC, Asio4All, free of charge, without additional hardware. It is highly recommended to install and use it.
ASIO option is not available on Mac ( but not useful, thanks to native low latency Mac audio drivers )