How bad are DVDRw drives for scanning CD-R discs?

I am aware that it’s generally not a good idea to scan CD-R discs using a DVDRw drive, and that this task should only be undertaken with an appropriately equipped CD-Rw drive.

So how bad is it really? Is there anything at all I can infer from CD-R scans done on a DVDRw? Or is it totally random?