BETA-2K wrote:
I am about to have a new asphalt shingle roof put on my house. It
now has one asphalt shingle roof on it and the decking underneath is
in good shape.
Other than it costing a little less by saving on the tear-off
process, is there any real difference between ending up with one roof
or two?
Even if it costs more, if there is an advantage to having the present
roof taken off first, I would do that.

I'd leave it and use the money saved to put in gutters - or some other
upgrade.