One of the cases where we often see this is when dealing with the so-called n-ary
relationships. These types of relationships are often hidden in the model when we
want to associate more than two things; in some cases, the natural and convenient
way to represent certain concepts is to use relations to link a concept to more than
just one concept. These relations are called n-ary relations because they can serve
more than two (in fact, n) things or concepts. It is a very common modeling pattern.
When we discover these types of relationships in a graph model, this typically means
that there's an additional node to discover that we have split out a new entity.