MDX - With Member

I saw mdx codes example using the "With Member" like1. With Member Test1 as ....2. With Member Measures.Test1 as ...3. With Member DimensionName.HierarchyName.Test1 as ....As far as I see #1 and #2 work the same, while #3 is different. But I am not clear what the difference is. More importantly, I need guidelines on which option I should use. Thanks.