it means that you will have one membership number (i.e. one contract is the master contract and the other will be a sub contract under that one). one contract will be ######.001 and the other ######.002 or something like that.
you can still sell or will the contracts separately but otherwise they will function as one contract (at 11 months out, if both have the same home resort, or at 7 months out, if they are different home resorts.) it's just an easier way to go...