Right now, it's impossible to safely hold corporate-scale amounts of money in Bitcoin, because corporations can't trust any one person with unrestricted spending power.
OP_CHECKMULTISIG makes it possible to have a transaction that requires several signatures (need 2 of 3 sigs from A, B, C). This proposal is to allow finer grained logic for when a payment is redeemed (A and B's sigs or just C).