get something called a "carbtune" it does the same thing as the mercury gauges, however it doesnt have the joyfull hazard of if you f*k up and give it a wristfull, you suck a few mg of mercury through your engine. That's 'cause it's got steel rods that get sucked up from their seats by the engine vacuum.
no adjustment needed, they all stay as accurate as the day they were made

. Used my neighbours ones a dozen times and never had any problems with them.
The ones you have just look bling

.
Carbtuning is synching the carbs as said before, so they suck in the same quantity of air / have the same air "vacuum", rated in inches of mercury, or in my case, inches a steel rod is raised

. having these off synch will vastly affect tractability, low throttle openings, fuel economy (as you'll always be trying to compensate for the "rough" spot), and all round smoothness, etc etc etc.
Anyhow, if your bike gets a bit rough off the line, definately worth getting em balanced.