Some small addition:
Sometimes you model an equipment in a location based on a channel of a device located somewhere else.
Example:
I have window contacts connected to a central knx binary input located somewhere centrally.
So I model the contact as an equipment in the room but link a point from the binary input thing.
The input itself is modelled as a separate equipment as it holds more information / channels than just the contacts.
My rule is to model an equipment, where the user would expect it to be located.
I really recommend reading the post by Rich, very good overview.
Thomas