Does this have any adverse effects?

historically none that I'm aware of, it just prevents it from logging into the back office, underlying services that use the account still work from what I've seen.

Ye i believe this too, dont delete it though 😉

Are there ootb underlying services that use the main admin account?

Nothing "runs as it" per say, but background tasks (scheduled publishing etc) I "think" associates entries against the "admin account" using the known ID. I could be wrong but I'm pretty sure that used to be the case and I don't think it's changed.

> I "think" associates entries against the "admin account" using the known ID. Not any more AFAIK! And we wouldn't need a user to be active for that, it was literally just logging the integer and not looking at anything else (too much overhead to look up a whole user).