Drop Subject..??

Drop subject..? is it the right ways for students when they are have problem with their academic..? sometime this is not a good ideas for a few students because it is about future.. I know, when we drop subject, we can take again, but there is can waste your time especially your age, because many institute cannot give kredit hour more for students, may be students can take twenty kredit hour for one season. However this is your decicions, which determine the direction of your studies you.