Pac-Man, while there may not be any problem with neglecting to obtain a marriage license, one must report total household income when applying for most (if not all) government benefits. So even if the married couple has no marriage license, if they are living together they must report the husband’s income. Given that this is the case, how exactly does the couple benefit by not obtaining a marriage license?
Unless you are referring to a polygamous marriage. In that case, by marrying without obtaining a license the husband could avoid prosecution for bigamy, but all household income must still be reported.