Well it depends what sort of things you are shooting and situations you may encounter.
Also, depending on camera if you could choose to use auto ISO (only works well in certain canon models).
Imagine shooting in a low light situation with fixed ISO, and a desirable shutter speed in tv. If the light level drops of the metered scene and the lens is already at maximum aperture with safety shift off the photo is underexposed. With it on, even though you are in shutter priority, once maximum aperture has been reached it will still expose how you've asked it to (metering mode/exposure compensation) by increasing the length of exposure.
The choice is weighing up the risk of an underexposed photo, or the chance of a blurry one and it really is up to you.
It also applies in av when maximum shutter speed is achieved (shooting into sun momentarily for example at a higher fixed ISO) by stopping down the aperture to prevent overexposure.
I used to have it on when I shot canon.