The other situation is, if you enter Orthodoxy via one of jurisidictions that do recognize certain non-Orthodox baptisms, and then later decide you want to join ROCOR, you would have to get baptized because they do not recognize even Roman Catholic baptisms.
There is a similar situation within Judaism, the religion of my birth. Orthodox (traditional) Judaism does not recognize any conversions apart from their own. Also, to be a Jew by their definition you must either have been born of a Halachically Jewish mother (one regarded as Jewish by Orthodox Judaism), or you have to have had an Orthodox Jewish conversion; Reform, Conservative, Reconstructionist, etc are not recognized.
I've known of cases of people who converted to Reform or another liberal brand of Judaism, who became more religious later and wanted to become Orthodox Jews, only to find they had to go through a conversion all over again.