One question I see in the forum a lot is “what is the difference between beeswax and Thread Heaven?” I got the best answer for this in a class with Diane Fitzgerald.
Beeswax is sticky, and is used when you want multiple threads to behave like one. So use it when you are using your thread doubled. It will save you from having to reposition your needle all the time at the end of the threads.
Thread Heaven helps keep your thread from tangling. It puts a static charge on the thread so the thread acts like your hair on a very dry day — the pieces move away from each other. This keeps the thread from wrapping around itself.