Can editing the UEFI improve stability or performance?

While looking into something else sort of unrelated, I stumbled in the bios modding community, but their explanations are mostly opaque, frequently giving no guides (what they do is that they let people request custom bios, and experienced modders make the new custom bios and give it to the person that requested it).

Seemly the most popular mods are:

• Replace AHCI.
• Move Windows OEM install between motherboards.
• "Fix" shoddily made ACPI device tables.
• Replace RAID drivers.
• Replace some other drivers.
• Replace AMI filesystem drivers with Intel's ones.
• Add operating system selector and bootloader.

I honestly have no idea what most of these are for (specially the lots of AHCI mods...), so I am wondering, why these people are doing this? Does it actually increase performance or stability? What UEFI drivers affect beside the boot process?