Only if you want 4K. For 1080P, you just buy a game as a product.
> It's really barely going to be cheaper than an Xbox and give you significantly less performance.
I agree that for the 4K Chromecast option to make any sense, it must be much cheaper than a conventional console. They would have done well to find a way to support existing (and cheaper) Chromecasts too.
There's also the PC gaming market though. Stadia will reach PC gamers on all desktop OSs, no additional hardware needed. There could be a market for people with laptops, for instance.
Incidentally, we've seen all this before with OnLive and PlayStation Now, which people seem to have largely forgotten about - nothing Google is doing here is new. OnLive functioned as both a microconsole, and an application on Windows/Mac/Android.