I think that the reason there are numerous answers is that community property states and common-law states get different correct answers for the same data. Different kinds of income or deductions or credits may not get good treatment if IRS cannot "see" the full family income picture. 

Here in TX it is rare for MFS to be beneficial. If the clients can talk to each other they normally file together and even if not talking (in divorce) they may still find a way to file together. I am sure that you have seen that in your years in the business.