What does the Engine Sync switch do?

[whitleybh2117]

I have Twin Merc 7.4 on a 40 Searay.

I have an engine Sync switch on my panel that I have always assumed was a dead switch as I did not think gas boats had that capability, I had always kept my RMPs as close to possible. I switched it while cruising and it did something to my RPMs

I have micro comander electric throttle and shifters and they are not even close to each others detent to keep the engines syc'd even with this switch which I just assume is a quarkiness of this boat. Just wondering what this switch is actually doing.

Thanks in advance for your valuable input