"Go with me."
Translation:Hãy đi với tôi.
Hãy is for politeness; think of inserting something akin to a 'please' in front. Without it, it sounds more like a command or an order.
That being said, a more pressing issue that if you then go on to insert and use 'hãy' later on in this course to make the sentence sound more agreeable, you'll likely be punished for it. So go figure.
Somebody from Hanoi told me that there is a sense of more familiarity with cùng, like for example you can tell to someone "let's go to the concert" but if you go with different groups for example, you would tell them "đi với", but if you went together, the person and you, then that would be "cùng".
Would this be a correct interpretation?