It seems common in physics papers & literature to simply point someone to a paper for a quite particular result in it, without giving a more specific citation. This often forces a reader to sift through 30 or more pages of material to find what they are looking for, leading to a waste of time for the reader.

For example, if you're referring to Theorem 17 or Eq. (134) in a paper, then cite it alongside the paper citation. This helps to speed up the job of the reader of your paper.