The only reasons you'll need the cable are:
1) The distance between them is pushing the limits of what's possible (I think they start complaining when they're about 4.5m apart)
2) They don't have line of sight between each other (i.e. if you wall mount them in the top corners of your room but you have a light fitting in the room that's blocking the view between the base stations then the cable will keep them in sync)
3) They don't maintain a line of sight because you walk between them (i.e. if you're using tripods that mean the base stations are only 5 feet off the ground then when you walk between them they lose line of sight and tracking will be affected)
If none of those are an issue you don't need the wire. I've got a setup that uses no wires (at my house) and it's been like that since the launch of the HTC Vive and worked flawlessly.
I've also got a setup in work where the base stations are over 5m apart, so we use the cable simply to stop the warning popping up that they're too far apart. It also works fine.