1) It would give you leverage over any police officer that might try to give you a ticket.
2) It'll make you feel less guilty about eating at Dunkin' Donuts each week, since you're just "reinvesting" in your company.
3) You can complain at the annual shareholders' meeting about the waitress that always messes up your order.
4) It would be the ultimate insult in your ongoing feud with Krispy Kreme.
5) You might finally be able to get some movement behind your idea of a "chicken half pounder donut sandwich."
6) Going on a donut eating binge could now be considered "market research."
7) If you're ever unhappy with the service you receive at a local store you could start screaming "I'm going to vote to shut you down!" (and when the police come to arrest you, you can refer to item 1 above).
Disclaimer: At the time of this writing I do not own, or plan to initiate any trades, in Dunkin' Donuts. I do plan to eat their donuts from time to time, however.