There are 2 advantages I can think of to getting the het instead of the visual.

1) - if you can't afford the visual, which may mean you literally don't have the money, or you would just rather use the money elsewhere.

2) - if you'd like the thrill of the morph popping up in a clutch of eggs almost like magic since you don't own a visual snake of that morph.

Not saying these out weigh the advantages of buying the visual, just more angles to consider.