I don't think they're generally necessarily, but those types of labels are useful to describe people who are very particular about their preferences. For example, there are bisexuals who would sleep with both genders but for whatever reason only go out with a person from a specific gender. So a man who would sleep with both men and women but only seek romantic relationships with a woman, etc. Such an individual might call himself heteroromantic so that other men know they're not up for a relationship.

I think the difference with your croc example is that romance is often intertwined with sexual attraction, but not everyone operates the same way. Clearly defining themselves with these labels can help prevent misunderstandings from the get-go.