Does a second coat of paint use less paint?

Does a second coat of paint use less paint? It took us half the time to do the second coat. The decorator thinks a tin will be 80% empty after a first coat. Whereas a tin would only be 10% empty if a new one is opened for a second coat.

It took us half the time to do the second coat. The decorator thinks a tin will be 80% empty after a first coat. Whereas a tin would only be 10% empty if a new one is opened for a second coat.