canonical and non canonical data in DW design

Hello,
I wanna know what is the real impact of representing canonical and non canonical data in a star schema.
I read that fact tables must have atomic data only. What about dimensions? Can they represent non atomic data, why and in what cases?
Thank's in advance.

Sure, dimension need not be atomic, in fact there is no notion of 'atomic' dimension tables.

By their nature they are almost always denormalized and their natural keys may be compound business keys. In fact, a junk or 'mini' dimension is made up of left over attributes so its natural key is simply the concatenation of its attribute values.