Why should I use the Letter Service at the Career Center? If you are applying to more than three schools, or you think you want your letters held for other opportunities (like law school) in the future, you should plan to use the Letter Service. Your letter writers will write one letter and fill out one form, rather than filling out a different form for every application.
You put your own reputation on the line when you write a letter of recommendation. If you feel you do not know the person well enough, or they are somebody you cannot in good conscience recommend, decline their request.