A very dry, brittle cork near the end where it was closest to the wine in the bottle may indicate poor storage of the wine (the bottle not on its side most of the time) and excess exposure to oxygen in the bottles since a dry cork is more permeable to oxygen.
The guest may even want to smell the cork for wine faults such as oxidation or other faults but it is very unlikely he or she can tell more from the cork aroma than from smelling the wine in the glass itself. If they want to smell it, let them pick up the cork from where you have placed it (at about 12 o’clock above their plate) and take a whiff.
Don’t hand the cork to them; just place it on the table where they can pick it up to examine if desired.