No problem my friend ask all the questions you like that is how you learn stuff.
By leaving the system with out any power for 12 hours or overnight you ensure that there is no way at all for code to be retained. Even when you pull the plug and clear cmos there is still current from the capacitors or residual charge in the actual materials where the BIOS and the system stores information. Information like the training that the CPU does to the ram. It is a fail safe if you like to leave the system off for so long.
Some folks will only do a few minutes and say it did not work. Then they bring their boards into me and I do a full CMOS clear overnight and the impossible seems to have happened folks the board works again.