I'm also wondering about this.
For screen monitoring of e.g. games, photo viewing with Gallery of QuickPix, or tv streaming using an app provided by my cable company
I understood Chromecast is supposed to be especially good at showing content in the cloud. I forgot the exact list of supported services... Things like YouTube, picasa, Spotify, radio streams, Netflix? In this case, your tablet "refers" to the content, and chromecast does the actual downloading/streaming. Screen mirroring was added as an afterthought, and last I checked (hmm, 6 months ago) subject to a lot of disclaimers, supported only on some devices.
I understood Miracast is true screen mirroring, but the few receiver devices I looked at, mention technical limits, like (example) 15fps, which makes me doubt their use for video mirroring.
Thus I haven't bought anything yet :-\
More testimonies of miracast & Chromecast users could be interesting!