They must be used always. But in daily life we sometimes omit them because we can understand without them. Perhaps your teacher thought you knew the usage of them beacuse the usage is very easy. So the teacher omitted them. But I think your teacher should have used them for beginners like you.

The punctuation signs in the written Korean are almost the same as in English. Some people, however, do not use it in their messages on internet or mobile, though.