what does command-alt-power combination do during startup ?

My MBP has a dead battery. It just takes a while before my company buys a new one ... but meanwhile, the computer is extremely slow. I have been explained by an apple genius that some process is telling the kernel 'hey, something is wrong here with the battery', and that the kernel tries to react unsuccessfully... and this endlessly !

I did try an OS install from scratch, which took a full day, but did not solve anything. I tried resetting the SMC, resetting th P-RAM ... and today, I found a post on a forum : "hold shift-ctrl-alt-power for a few seconds, and then cmd-alt-power" ... and, guess what ? It works ! But now, I am wondering : What am I doing whit this magical combination ? Any side-effects have to be expected ?

thanks in advance

xavier