Why is the --run required while updating the firmware ?

[hrtk]

Hi.
I was successfully able to remove the 5 seconds delay. (http://digistump.com/board/index.php/topic,320.0.html ) Though, I do have a question. Why do we need to pass the `--run` argument to micronucleus while uploading the firmware ?
Don't we just want to flash the firmware and not run it at that time ?
Why does it all go crazy (http://digistump.com/board/index.php/topic,320.msg8546.html#msg8546) when we don't provide the --run argument ?
Also, while trying to flash another firmware after this, would I need to connect P0 to GND ?