Here is a link from a previous blogpost including a webcast from the United States Golf Association which better explains covering greens.
So much like you or I need a coat on when it gets cold outside, our greens do also, especially this year with the warm weather and the extended growth of the grass. Covering the greens will increase the temperatures under the covers from 5-8 degrees higher than the temperature outside of the cover. This may not sound like much but that slight increase in temperature can be the life and death of ultradwarf greens. It takes a little work to protect them but it is worth every second in the long run. And it is still better than syringing bentgrass greens all summer long.