I think it boils down to why we study languages, our goals and our personal interests. Personally I am not that concerned about whether I meet someone else's standards. I tend to agree with Marianne that trying to master any element of grammar slows you down. On the other hand you need to have some acquaintance with the basic grammar patterns, or at least what to expect. In other words, for Russian, to know that cases exist and in many cases replace the function of prepositions in English.
Evgueny has created an excellent series on Russian grammar, all in Russian. These are texts we can listen to and read again and again.
I am more motivated to read and listen, and acquire words. I refer to grammar occasionally and repeatedly. Evgueny's resources are great for this and I also refer to tables. However, I don't believe that "mastery" is a realistic goal for a variety of aspects of grammar, at least until we have had a lot of exposure to the language. I know many fluent Russian speakers of English who will never "master" the use of articles. Other than on a grammar exam, this does not prevent them from enjoying the language and communicating effectively.