I know it's a little bit of an old topic, With older (worn) carbs (and an engine with wear on it). the sync at idle doesn't mean the slides are even. Going back a couple of years, I vacuum synced a couple of my Z1 carb racks with gauges - got them perfect. When I looked at the gaps under the slides, they were all over the place - which means you get uneven fuel delivery though the needle/needle jet. at 3,000-5,000 RPM - where you spend a decent amount of your time riding What this really highlights is the wear on the carbs (or on the engine) If a cylinder has slightly lower compression, it's not going to suck as much air/fuel through the carbs... plus, you should always check/adjust valve clearances before syncing carbs.
I want my carbs synced for smooth running while I'm riding and will put up with a little bit of a rough idle.
By all means use the sync gauges, but visually inspect the slide heights - I think some of you will be surprised by how far off the slides are from 'synced'.
The other thing with slides, make sure at wide open throttle, all the slides clear the bore. When you mess with the individual carb adjustments, you can stop slides from fully clearing the bore..