If you sell the same room on your own website and on one or more booking sites, something has to tell each of them when a night is sold. When nothing does, two guests book the same room, and one of them gets a phone call nobody wants to make.
There are two ways to pass that message along, and both are sold under the same word: sync. They move very different things. iCal sync moves blocked dates, after a delay. A channel manager moves availability, rates, restrictions and the reservation itself, as they change. Which one you need depends on your property, and for some properties the lighter one is enough.
