Someone called in a question to Catholic Answers, on the radio. The caller wanted to know why Catholics can't have their ashes scattered, after they died. The response had to do with our bodies being temples of the Holy Spirit and as such should be treated with respect.
I wasn't satisfied with that answer. I would say that the church desires our cremains to be buried in sacred ground. The human body is the temple of the Holy Spirit and as such, should be treated with as much respect as possible. To ensure that the cremains are respected, they should be placed in designated holy areas where people come to pray, places that have been consecrated, like a cemetery.
Scattering ashes in the ocean goes ??????????? Placing ashes in favorite places doesn't ensure respectful treatment.
I'd say Mother Church knows best.