Is there a general principle for how we treat a י"א = יש אומרים (yesh omrim, "some say") cited in the Shulchan Aruch for the purposes of determining halacha? If not, are there examples of two halachos where we use different approaches towards a י"א (e.g. following one but not the other, treating one as going l'chumra and one as going l'kula, etc.)?
Synopsized from Yad Malachi (K'lalei Haposkim - HSh"' VRM"' #13,14,16,17):