Can area rugs discolour hardwood floors?

Q: Can area rugs discolour hardwood floors? I was told by a rug salesperson that rugs could discolour hardwood floors, especially new hardwoods.

She said carpet pads alleviate the problem.

A: I have heard that certain backings and pads can leave a residue that will make it difficult to coat a floor. The sun does most of the discoloration.