Scans are analyses of how much error correction is necessary for the drive to read the disc.
Less error correction == better quality burn
You can use the scan results to check how good your media is, screen for failing media, see how well your burner performs, etc.
To use KProbe, you must have Lite On drive. Check out the KProbe 2 Thread if you are interested.
There are a few other drives that can do the same thing using other utilities.