We often here that Canon had to ditch the FD mount in order to get AF working, what advantages did the EF mount bring and what exactly are the pros and cons of lens mounts by Nikon, Sony, Pentax and others ?
I haven't heard that they needed to do it to get AF to work, but a complete new design to accommodate the electrical connections and eliminate the unnecessary components, as well as making the mount larger in diameter has proven to be a good choice over the years.
The EF mount was almost certainly less expensive to build, which probably had a lot of influence on the decision to change. Mounting rings are made to incredibly tight tolerances, and the complex mount used on the FD was certainly more difficult to build. It was also a better mount in that it was secure and would not let a lens rotate even a tiny bit when tightened down.
The bayonet mount was larger, and made it a bit easier to fit the electrical contacts into plus, some say it allowed for wide aperture lenses with less viginetting, but I'm not sure that's entirely true.
What is bad about it and all bayonet lenses is that they do not lock a lens securely in place. The lens can rock back and forth due simply to tolerances. My Nikon lenses do the same.
One thing in its advantage is that every EF lens will mount and work on every EF or EF-s mount. I need a book to carry along when looking at used Nikon lenses to see which ones can be mounted and what features can be used. Some of the older ones will cause physical damage to modern Nikon cameras, its a nightmare to those who want to purchase old lenses to use as manual focus lenses on a new digital body.
With Canon, its simpler, just don't do it unless its a lens worth adding a high quality adapter like those Ed Mika makes.
Most of the camera makers have changed mounts one or more times over the years, so you need to be a expert on a particular model. For adapting to Canon, the M42 mounts is very easy, because they had a push in button on the rear that stopped down the aperture, and screwing on a adapter pushes the button in, so that you can manually change apertures easily.
I'm sure there are a ton of details that were argued back when the change took place, I've forgot most, except that photographers were very upset over losing the breech lock mount which was considered to be superior. . There were some lenses that were bridge lenses and did not have all the EF features. Even a couple of electric zoom lenses with push buttons on the side to zoom. That was a bad idea, and quickly went away.