You care when the lecture with the better professor conflicts with another needed course or is filled with higher priority students. Even if you register for the section with the sucky prof and are able to sneak in unnoticed to the lecture section with the good prof, you care if the multiple sections do not have common exams. You care when you can’t pop into any recitation section if you’re not registered. Or at my college, you’d care because your choice is to take the one lecture section of orgo offered or not