This is a good question! And one that is brought to us quite often.
First of all, streaming games with Antstream Arcade allows you to play anywhere, at any time, and pick up where you left off.
It is completely FREE, licensed and legal. You can game guilt-free knowing that publishers are receiving credit for their work as well as protecting your own PC from downloading illegal ROMs on the internet.
Some people don't want to mess around with emulators that may be difficult to set up, or just download illegal files in general. Antstream offers a pick-up and play service that is licensed and fair for everybody! :)