Add me to the +1 for having a built-in scheduler. It's useful for plenty of things like automated partition creation (as noted), scheduling backups, index maintenance, batch processing jobs, etc...
I wrote jpgAgent (compatible with pgAgent) ~10 years ago because pgAgent was too unstable (and the other scheduling tools hadn't come out yet), but I really wish I didn't have to deal with external tooling for features like this at all.