I bought the ESA on the day when I bought my car to the service center with what at the moment appeared to be a failure of the MCU. The SC was telling me to expect to need to replace it. That was the last day on which I could purchase the ESA (30 days past end of warranty). At the time, the MCU replacement was something like $2500. It turned out that I did not need the MCU that day, but I did need one (because of the eMMc memory issue) a few months later. At the time, the fix was replacement of the MCU with a rebuilt unit, including the screen itself. So I felt like I had avoided paying the fee for that (which I think was then $1500). Of course, not long after that, an even cheaper fix was developed. And not long after that, the MCU issue became the subject of a recall with the prospect of a free replacement of the memory. so my initial decision to buy the EAS might have been driven by the fear of a large expense that I did not actually incur. In the meantime, I had a failure of my parking brake caliper. The SC replaced both. They told me the retail cost, which would have been north of $1000, so again I felt as though the ESA had helped me dodge a big cost. Since then, I have had one door handle repair plus replacement of the windshield washer pump. In the last two cases, the $200 "copay" was probably about half of what the repair might have cost at retail.
So, in the 18 months since I bought the EAS, have I saved any money? Not literally, I suppose. Leaving aside the MCU replacement, the covered repairs would have cost something over $1500, so I have a long way to go to recover my cost.
I can cancel the EAS at any time and receive a prorated refund of the unused portion. Or I can keep it for the peace of mind.
Every week, I read about Model S problems that I have not yet experienced, so the potential is there for more failures. But as others have said, it is absolutely a question of odds -- No one can know what will or won't break until it happens (with the possible exception of door handles, I suppose).