the REFERENCES privilege is only about creating a foreign key constraint? Practical use cases?
If you have the ability to create a foreign key constraint, you are actually getting permission to check for the existence/non-existence of a certain value in a certain column (or set of columns) of a table. You may not have the privilege to SELECT the whole list of values in this column, but you can already know something about them. You could try to insert values on the referencing table. The ones that are allowed, you already know exist in the referenced table. 

If you should know absolutely nothing about those values, you cannot be granted the privilege to make a foreign key constraint on the column. 

Add to that the considerations pointed out by @Erwin, WRT to being able to prevent deletes from the referenced tables.