The Chromecast can do a lot, but until today, you needed your smartphone to control what you're watching. If your TV has HDMI-CEC support, though, you can now use your existing TV remote to play or pause videos.
You've been able to power on your Chromecast with a remote for a while now, but a new update is rolling out to Chromecasts that enables play and pause, which is insanely convenient. Your TV will need to have HDMI-CEC support to make use of it, but many do these days -- so if you aren't sure, check your TV's manual or Google around. (It may often go by another name, such as Samsung's Anynet+ or Sony's Bravia Link.)