As a flight instructor we’re always impressing upon our students to read back ATC instructions so there are no misunderstandings.
I was flying around the traffic pattern with my student one busy afternoon when an aircraft called the tower seven miles out for landing. The pilot sounded nervous on the radio, but was doing a good job. He was making the proper calls and reading back instructions, almost verbatim. After sequencing the pilot in and delaying his clearance to land till short final due to traffic, the controller, realizing the pilot was very busy landing the plane, said, “Cessna 123, no need to acknowledge. Runway 3, cleared to land.”
Sure enough, relying on his training, the pilot read back, “No need to acknowledge. Runway 3, cleared to land. Cessna 123.”