I guess it depends on what bothers you more, tearing or input lag. I tend to game with it off for the most part, so as to remove the laggy input from the mouse, although some games are really horrible with it off (Crysis comes to mind). One of the ways you can help to reduce it is by turning on Adaptive V-Sync on compatible Nvidia cards. Below is the explanation taken from their site on how it works:
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Adaptive VSync
Nothing is more distracting than frame rate stuttering and screen tearing. The first tends to occur when frame rates are low, the second when frame rates are high. Adaptive VSync is a smarter way to render frames using NVIDIA Control Panel software. At high framerates, VSync is enabled to eliminate tearing. At low frame rates, it's disabled to minimize stuttering. For a superior solution, which eliminates stuttering, tearing and the addition of VSync-related input lag, see our G-SYNC technology page.
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I'm not sure if AMD has the same feature on their cards or if it is specific to Nvidia users. The other alternative around tearing and stuttering (although not necessarily input lag) is to buy a compatible G-Sync monitor which has a V-Sync which is variable and adjusts to your card's framerate accordingly. From what I have heard it does a fairly good job of it for the most part. I think this is only compatible with Nvidia users, but don't quote me on that. Apparently there are also G-Sync adapters, but I don't know how widespread they are, or how compatible they are with the enormous range of monitors out there.