A vacuum gauge will tell you more than just balance. You can [and should] use the vacuum reading to set the idle mixture. A weak or erratic signal can help you pinpoint a bad ignition, leaky or sticking valve, vacuum leak, etc. Plus, with gauges there is no chance of sucking a cylinder full of oil when the balance is too far off.
The biggest advantage to the gauges is that you can mount them to the handle bars and see what the vacuum looks like while motoring down the road. That is what allowed me to zero in on the sticky slide in my PWK. I was able to see which slide was sticking and exactly what throttle position it was sticking at. There was also a noticable improvement when adjusting the dual cables based on cruise vacuum instead of the crack-the-throttle-in-neutral vacuum. The engine runs smoother, shifts better, and sounds cleaner.