What was the motivation to add those cameras to Perseverance? Were they needed for the landing manoeuvres (I doubt it, as they were covered until the rover was lowered)? Did they allow to learn new things about the sky crane operations that were not yet learned from Curiosity's successful landing? Or was it just a PR gimmick that was evaluated at lots of good PR for little cost?
The cameras were added so that the engineers can see if everything happened as expected and to inform the technology of future landings. They also serve a public relations use:
While extensive reconstruction of the entire EDL sequence can be done based on telemetry and MEDLI2 data, some phenomena of EDL are best depicted through sight and sound. For example, the dynamics of parachute inflation are complex and nonlinear, and cannot be fully resolved using acceleration data recorded by the IMU. EDL Cameras were added to the Mars 2020 mission in order to improve engineers’ understanding of events like these, as well as adding to the public’s excitement about the climactic events of EDL.
The videos might also have scientific use:
Although EDL camera images are intended to be used for the engineering assessment of EDL performance, it is expected that images of the surface from the RDC and LCAM may also be of scientific interest (dust plumes, disturbance of rocks/fines, etc.).