Paskening Din (Monetary Issues) Vs. Paskening Issur

 The Gemara in Bechoros (49A, Niddah 64A, Eiruvin 93B) says that when Rav argues with Shmuel we pasken like Rav with regard to Issur. The Ros'h in Perek Hazahav says that in Dinim we pasken like Shmuel. 

The Rosh in Bava Kama (4th Perek Siman Daled) explains simply that Shmuel was a Dayan and therefore more proficient in Dinei Mamonos while Rav was a Posek and therefore more proficient in Hilchos Issur. 

The Chavas Yair (Siman 94) says a very interesting chiddush. The Chavas Yair posits that Rav, who is Tanna Upalig was a buki (expert) in Mishnayos and Braysos and had a very wide breadth of knowledge to the extent that he had the authority to argue on Tannaim. This breadth of knowledge was so great that when he argued with Shumel we always paken like him (Rav). Shmuel, on the other hand, as it is well know was  an expert doctor and moreover, as he himself stated, very knowledgeable in Astronomy and other sciences. Shmuel, states the Chavas Yair, was not as big of an expert in Mishna, Braisa, Tosefta, as Rav but rather had a much more well rounded education. Therefore, when it came to Halacha we pasken like Rav. However, regarding Dinei Mamonos (Monetary issues) having a sharp mind and the ability to analyze a situation allowed Shmuel to be better equiped to pasken Dinim. 

In short, the Chavas Yair seems to be saying that for Issur for Heter you need to be a "Sinai" and the bigger "Sinai" one is the more we can rely on him for psak. However, for Dinim you need to be an "Oker Harim" (one who keen analytical abilities) and Shmuel, although he didn't know as much as Rav, had better analysis tools. The Chavas Yair also adds that the fact that Shmuel had a proficiency in these other disciplines gave him an edge in paskening Din. 

There is much more "Svara" in Choshen Mishpat than there is in the rest of Shulchan Aruch. Halachic knowledge without keen Svara can only get one so far regarding Choshen Mishpat laws.