in short: JTAG is a direct connection to the processor, for debugging, monitoring, programming…
If anything goes wrong while flashing the backup file i posted (power loss,…) or it´s simply not compatible to your hardware revision (i think it wold work for all revisions but I DON´T KNOW…) it may be possible that your dso would not start anymore and you won´t be able to flash a new firmware the normal way.
in such a case you could use a jtag interface cable and a piece of software to access the processor directly and so programm it´s internal memory.
I think if if your battery is full, usb cable and power switch stays untouched during flash, the risc is minimal.
but that minimal risc is yours