What happens if you don't?
It's perfectly safe to throw the switch while powered up. I've done so hundreds of times (A500 and A3000) and after all, it just toggles a bit flag.
However, it won't have any effect until the next reboot.
Contrary to common belief, it's also quite 'safe' to switch Kickstart ROMs, the A19, or the _EXRAM option while powered up. 'Safe' in the sense that it won't cause any permanent damage but only crash the system violently.
