By giving someone a graceful way to decline, you may save yourself a lukewarm letter that could weaken your application. If you trust your recommender, then check the box that says you waive your right to see the letter. The confidentiality makes the letter appear more valid and honest. If you do not trust the recommender, then ask someone else to write for you. This information will help the person write a more detailed letter.
Programs are more impressed by a letter from someone who knows the applicant well.
Be sure that you have filled out all parts carefully and completely. Use a typewriter to type your name and everything else on the forms and envelopes. Provide stamped envelopes with typed addresses to your recommenders. Provide the recommender with all materials in a neat, easy to read package. This will help the recommender keep track of things.