UEFI allows you to programmatically change the boot device from inside the OS. This is important for failed or degraded SSDs, as they can fail in weird ways (read only, all reads hang, etc) such that trying to boot from them can hang the system. That allows you to detect a failing boot driver, and gracefully fall back to booting from another mirror/raid member and avoid having to have somebody touch a server by hand.
There are plenty of other firmware systems that allow for the same thing, and I dislike UEFI as much as the next guy, but this is a feature that's been important at work.
efivars is probably the goofiest and most uncomfortable way of handling this. They created this giant wasteful infrastructure in EFI and at the end of the day, you're still poking around in a bespoke filesystem to hopefully communicate GUID tagged facts about your boot drives to your bios.
There were tons of other ways this could have been accomplished for far less effort and with previously existing systems.
There are plenty of other firmware systems that allow for the same thing, and I dislike UEFI as much as the next guy, but this is a feature that's been important at work.