Let’s you stream your cable from your house to your laptop/desktop anywhere you get internet access. In essence...whatever is playing on you home tv you can watch on your computer elsewhere.
I used to travel to Europe for business and had a Slingbox hooked up to my satellite receiver at home. It let me watch remotely on my laptop from anywhere I had a good/fast internet connection. Believe me, when you’re in a London hotel and your choices are BBC-1 through -4, Skynews, and 10 non-English language channels, you get bored quickly!
(created some interesting challenges with “she who must be obeyed” when I’d be operating the tuner from far-away, but that’s another story!)