Platelets are small cells in your blood used for a multitude of reasons. They can be used to form clots to stop bleeding, fight cancer, and dealing with serious injuries. Platelets can be donated every 7 days, which is necessary if you can sinced they have to be used with 5 days from the time you donate! The only downside for donating only platelets is that it can take a bit of time, about 2 to 3 hours of your day, which is another reason why platelets are always in demand and why blood banks typically offer more incentives for platelet donations over blood donations.