Okay, I know this is a pretty fundamental question for this forum, but... why do you use syncros on multiengine aircraft? What's the benefit?

I've been flying a Twinstar this summer, my first twin, on 2 OS .28 heli engines. To date I've not yet been able to understand what the benefit of a synchronizing device for the two engines would be... Is it maybe more of a requirement on larger engined aircraft?