You may find yourself in that situation if you have a device that only supports SIMs, and you can't use any of the cheap travel esim providers with it. For travel, you would replace your local SIM with the 9eSIM, and be able to switch providers depending on destination. The difference can be huge in some countries, where a local provider's travel plan can be 30 to 50 USD, while a equivalent on an ESIM provider is just $4.

I live in such a country and have parents with older phones who can't use esims, so the value is obvious to me. :)