To make it further clear:
If you are Marco Polo (MPC) member, you are automatically enrolled in Asiamiles. However, this does NOT mean there are seperate accounts and/or membership card. Your MPC membership # and asiamiles membership # are identical.
When you fly, your asiamiles credits, or so called "points", will be redeemable for future travel. However, no matter how much asiamiles balance you have, it will not give you any benefits.
That's when MPC comes in. Your status credits, which are your ACTUAL flown miles, will be credited in your MPC account simultaneously. These MPC credits are NOT redeemable for awards. Think of it as a log of how much miles you've flown to date. THEN, depending on how much MPC status credits you have, your membership level is determined. For example, if you have 30k status credit, you will be a silver member, enjoying lounge and checkin benefits and various others.
Asiamiles balance will only be reduced if you claim an award, but your MPC credits will be reset to 0 every year. Also, many of these "double miles offer" only apply to earning of Asiamiles, but rarely is there any bonuses awarded to MPC status credits. (unlike AA's elite bonus)