MOOC's certificates on graduate admissions
You're free to mention the certificate in your application.  How much weight to give to it is presumably up to individual committee members.  I think unless the certificate pertains to a specific skill that's in demand for the program, you shouldn't expect to get much of a boost from having one.  At the moment, people don't have much experience with such certificates, and will be more inclined to look at indicators they know better, like grades and GREs.  It's possible this will change a bit in the future, but it will likely move pretty slowly.