I have Gsync, I think it's a nice touch.
But yeah objectively speaking it is overkill - sort of. You might potentially get tearing here and there but it would be unusual. Thing is, with a 144hz monitor, gsync makes more sense than with a 60hz monitor, since your frames may be in the 120 fps and unable to reach the monitor's refresh rate.
If the monitor you like happens to come with Gsync, go ahead and get it, but don't go out of your way for Gsync. I personally use it when I'm hitting 50fps and my monitor outputs 144hz.
If you want to play casual games, go for a 1440p Gsync monitor instead, but if you're playing eSports like CS:GO, get yourself the 1080p 144hz.
Source: Own a 144hz 1080p Gsync monitor.