Is there any point in adding a non-Steam game to Steam?

Having everything in one launcher is nice, but the big advantage is that it will try to enable the steam in-game interface. This isn't always a good thing - you may want to disable it for some games if it makes them unstable.

Launching non-steam games from steam will also display to your friends that you are playing that game. For me, this is a critical feature. It will not track your play time on that game, however.

Update: You can now in-home stream non-steam games if you add them. Thanks to the other replies for mentioning this.

The advantages (already mentioned) are that you can have all game shortcuts in one place, other people can see you playing that game and you have Steam overlay in-game.

There are also some disadvantages. If you are downloading or updating a game on Steam launching the non-Steam game stops the download/update; this is the default behavior of Steam. Useful if you are playing a multiplayer game, but annoying if you are playing a single player game.

But the main disadvantage is that not all games are compatible with Steam overlay. Just as example I can cite League Of Legends. If you try to chat during game the chat stoles the focus and you game does not get anymore key inputs; the only workaround in this case is Alt+Tab to desktop and than return to the game.

Non-Steam games added to Steam can be streamed with In-Home Streaming.

This way you can let your ever eager to play friends know what you're busy doing besides games. Sometimes I'm playing Microsoft Visual Studio 2017, so everyone knows I'm not really up to much else at the moment.

Also, it's fun to be playing ridiculous non-game stuff. And games are about fun, so it's a nice feature.

Having all your game library all in one place has the advantages of having only one launcher which can lead to a cleaner desktop. It allows you to remember those older or indie games you don't play as often anymore.