I don't really think it's a grammar related problem, it's more related to our life experienceXD so different Chinese may give you different answers. I tend to describe the situations which I will use or I heard of others used. Same thing is that you are busy and think of whether you should go...1別去呗--your roommate can no longer tolerant you keep walking around and nerves and still cannot decide, she think it's definitely not a big deal whether you go or not. that's the time she will use this. ‌2别去嘛--嘛usually used by women. Pretend you are a guy promised your girlfriend to take her out for dinner. Suddenly, your boss asked you if you want to go dinner with him. It's a good chance for you. Your girlfriend don't want to to go. She will use this to act coquettishly. ‌3别去吧--your friends invited you to a nightclub. Your parents are worried they are bad persons, but you are adult, they can only try to persuade you not going. ‌I cannot type any longer... italki has limits

These subtleness in the language sometime make it difficult when you start communicating with a person in Chinese and hope to be 100% accurate in understanding what does this person has in mind. But I suppose it can also be fun once you know the language well : )

Thanks Eddie! I think between your and Ruby’s explanations (plus any others who may comment) I can slowly begin to clear up some of these differences

Rebecca, I doubt I can give you a clear explanation, let me try nevertheless : ) 你很忙，别去嘛！you are busy, then don't go. (a stronger suggestion) 你很忙，别去呗！you are busy, then don't go! what's the big deal? (a casual suggestion) 你很忙，别去吧！you are busy, don't go (a suggestion) 吃饭呀！ 吃饭啊！eat! (could be from a strong suggestion to a mild instruction) 吃饭吧！why don't you eat! (a suggestion) 吃饭呗！just leave whatever you are doing and eat. what's the big deal? (a casual suggestion) Again, hopefully someone more professional here can you give you better answers : )