[Christ]

I didn't see even a slight delay in the restart, honestly. I hit the gas as I was turning the key, and it seemed like the engine just picked right up.

Rebooting a car's ECU is NOTHING like rebooting your home PC, or even your cell phone. It doesn't have a GUI, or any of the "cool" features that anything else has. It uses a very minimalist OS, which only contains the information necessary to run the software, and it's hard-coded in flash memory. Literally 1/60th of a second is plenty to start it back up.

Imagine your digital wristwatch... you put a battery in it, it's ON. Right now. No waiting for the software to become aware of what needs to be done, in a flash, it's there, working, telling you the time. (It's the wrong time, but that's something different.)

Now, as to whether the ECU will appreciate being turned on and off constantly, is a thing to consider. Over time, heating and cooling cycles help to cause "Tin Whiskers", a phenomena common to circuitry, where a circuit will grow a "hair" of tin that connects to another circuit and shorts it. Often, they will short, destroying the whisker, and not damage anything, but occasionally, they will destroy a circuit completely.

Another thing to consider is that over time, circuit lines wear away. They actually get thinner with use. What eventually happens, is that the line gets too small to deal with the current present in the line, and it eventually breaks the circuit. This is also not repairable, as it usually occurs on inner planes first, and could only be fixed by making an identical, external circuit on the board, using the VIAs that were connected to the broken circuit line.

By all means, leaving the ECU on for the drive instead of constantly shutting off/restarting will definitely prolong its life, but even in the event that it's dead, for most cars, its' a matter of going to a junkyard and paying $60 for a new one. When you consider the average of something like 3 starts a day that a car goes through, over the life of nearly 23 years that one of my cars has on it, that's A LOT of starts and stops that the ECU has gone through, and it still works. Even cut that time down to a couple years between replacements, and you're still on a good mark.

Spend $10 on a switch and a relay, and you're even better off, nearly never having to replace either, and saving the ECU all but the initial starts of each trip.