I don’t think there’s a ton of benefit to the technique. If you’re worried about getting too close to your certificate expiry via automation, the solution is to renew earlier rather than complicate things with a ladder of valid certs.
There are reasons to do this, just not because of expiry.
The main reason to have multiple certs is so if your host (and cert prov key) is compromised, you can quickly switch to a backup, without first having to sort out getting a new cert issued.
If you want a backup system its best if its self contained. When your site is down its easier to just run a single command to copy over a single file in your control instead of depending on an external service.
