in essence the IDR is the borrowing cost MWE/LP's (unit holders) will be paying for capital access ie vs debt or equity issuance or going to new partners for financing. pretty slick move
in the end it will be counter balancing-scratching each others back. helps mwe during low liquids prices ie capital available from a refiner who gets price advantage of differential in WTI-Brent now at a competitive NPV cost of captial (annual idrs); then later when differential contracts MPC shareholders will benefit from MWE increased cash flows to pay dividends, etc to overcome their margin contraction