One of the things that Apple TV has been used for a lot is to mirror the display of a late model Mac or iOS Device. I was actually curious about the Chromecast when it came out, so I ordered one. The idea behind it was that once you connected it to your HDTV you could display any tab/window from the Chrome browser on your TV. There are a couple of advantages to this approach. You could keep working on your laptop in other tabs or applications while the content from that one tab streamed to your TV. It didn’t dawn upon at the time that I actually already had this capability with my Apple TV (2nd or 3rd generation). In Mac OS X Mavericks and Yosemite you can display your Mac on your HDTV via AirPlay, but now you can actually turn off mirroring and use your Apple TV as an extended desktop. This of course means that you can put any window, application, browser window, etc. on your TV while the rest of your Mac is free to work on your other/main display. So if you wanted to watch an internet video on your TV, just AirPlay your Mac to your Apple TV and then just choose “Extend Desktop” from the AirPlay menu on your menubar.
Your sound will also be played through the TV or whatever audio system you have connected to your Apple TV. If you don’t have the AirPlay menu on your menubar then chances are your Mac is not new enough to support native AirPlay. In that case then the Chromecast might be the way to go.
You can get the latest model Apple TV on sale here.