Not Failing 

This one might sound pretty obvious but it's super important. Not failing is probably one of the best and most important reasons you could have for dropping a class. Whether you're a bad test taker and the class is comprised mostly of tests, or you missed that one assignment that was worth most of your grade, if you know that passing the class is next to impossible and it's still early on, might be the best case to drop that class. This way not only does it not affect your GPA, but you can also plan what to do next time to try and prevent it from happening.

Personal Issues

Now I'm not talking about a bad breakup or some sort with friends but really intense issues that can essentially throw your whole schedule off course. So, instances like a family emergency - a death in the family or even mental illness. Sometimes life gets in the way of our academics, and there isn't much we can do about it except brace for impact and hope we are left standing after it's over. If you find yourself having to devote all your energy into whatever is going on in your life and you just cannot do school at the moment, you might drop a class or just take the semester off and make it up after everything has settled down.

Difficulty 

Sometimes you get into a class and you think you know what's going on, but ultimately you are just really lost. It may be time to drop the class. Now I'm not saying this should be your first option. First, you should talk to your classmates, a teacher, or even a tutor to see if you can get a better understanding of the material. However, if that doesn't work, maybe you can try different modes of learning like audio files on the subject or even a YouTube video. If it's a course like a foreign language, maybe you should go down a level and see how you do in there. If you're on a beginner level and you have no clue what's going on, don't worry - 9 times out of 10 your classmates are in the same boat and you will learn as you go. Also, if it's a required class like a general curriculum one, in this instance, you just have to suck it up and do what you can. Even if you drop it, you will have to take it regardless; so, you really are just prolonging the torture.

Too Many Classes

As you progress through school, you will find yourself taking more and more classes. Sometimes the class workload differs enough that you can manage to get your assignments done and still relax and hang out with your friends - that's great. However, sometimes you end up taking a lot of classes that all give out an insane amount of work for each class every week. If that's the case and you start feeling overwhelmed like you are drowning in assignments with little to no sleep, it might be time to drop one. Working hard is a great quality, but overworking yourself till you are dead on your feet is not good.

Too Early

For me, I feel like it's better to just avoid this all together; but, if you can't and you end up regretting it, you might need to drop the class. I know that I have personally forbidden myself from ever taking an 8 am class. I am just not a morning person and I will never be one. You might have no trouble waking up at 8 to get ready for a 9 o'clock class, but getting up at 7 for an 8 is just not feasible. Unless you drastically change your sleeping habits (let's be real you won't), then your better off dropping the class and finding a different time than failing because you couldn't get up in time to make it to class.

Teachers

Now, this isn't always a good reason but sometimes it makes the most sense. For me personally, I know that I learn better when I can get along with the teacher or at least coexist together. However, there are some teachers who I just can't stand and if I could go back and avoid taking them, I would. Sometimes you sign up for a class and you just can't get with their teaching style or they always feel the need to target you. Then why make yourself suffer. Or if you just can't understand what the teacher is saying no matter how many times they've said it, and even your classmates are confused you may be better off finding a different teacher for that course. If you have the option and it's not like at the end of the semester, then go for it and say sayonara.