Measures in Dimension table ?

I have heard that measures (amount fields) does not belong in the dimension tables but is that a rule of thumb ? Are there exceptions to this rule ? How do we decide if a measure belongs to Dimension or Fact table ? Lets say I have a dimension (campaign) which has some amount fields(like margin amounts) attached to it at the dimension grain and they rarely change. These fields are decided upfront. Now what would be the drawbacks of keeping them in the dimension table? If it does not belong in dimension do we need to create a fact table just to analyze these ? You can't slice and dice these anyother way I think.

Appreciate your time.

Do you sum it or count it? If so, it's a fact otherwise you can put it in a dimension.