Its architects hope to prevent mistakes and their attendant morbidity and mortality. Regulators are also concerned with the way Medicare funds are spent since residents' salaries are indirectly drawn from these monies. If a resident performs a procedure that an attending does not supervise yet submits charges for, then Medicare is paying twice for that procedure. That practice could reasonably be labeled fraud or abuse. If a military contractor practiced that sort of government billing policy, few would defend it.
Independence has educational value, however.
This is especially true in surgery, where there is no substitute for actually performing the procedure. William Halsted, the father of modern surgical training, advocated a graduated increase in responsibility and independence for residents. If my attending is by my side for each of these maneuvers each time I do them, I may still learn but I will not learn as quickly or perhaps as well. Independence with a safety net lets me feel the anxiety of responsibility while protecting the welfare of my patients. Unfortunately, there is no reliable way to quantify whether and how any of these changes will actually affect the performance of those graduating from these residency programs.