Do graduate schools care if letters are confidential or not? In general, graduate programs prefer confidential letters. Admissions officials say that it displays more confidence on the part of the applicant if letters are "confidential" (meaning you, the applicant cannot see the letter). The Letter Service is required to indicate on the letter if it is confidential or non-confidential.
The most effective letters of recommendation are written by professors or work supervisors who know you well enough to describe your academic, personal, or professional achievements and potential with candor, detail, and objectivity. Letters that compare you to your academic peers are often the most useful. Most schools do not consider general, unreservedly praiseworthy letters helpful.