It is a waste of time and money, a typical Home Office exercise. Either you are married, or you are not. If you are, then it's for life, and no further visas for the foreign partner should ever be required.
I want to see the law – or Home Office regulation – scrapped that says a marriage between a UK citizen and a foreigner becomes invalid after two years. When you've already filled in a lot of paperwork, twice, and paid vast sums of money for precious little service, it is offensive to be made to do it again.