Owing to the fact my chemistry teacher is ill and/or is slightly incompetent when it comes to time management, I had a chemistry revision day last Friday with one of the chemistry teachers at my school who happens to be an examiner (of some description for our exam board).
In any case, he recommended using bullet points but ensuring that answers were written in full sentences.
One example he gave us was literally one sentence split into three sections with bullet points attached to the front. To be honest, I couldn't really see the point of it since it was only once sentence but he was adamant that examiners liked it since your points really stood out. (He also recommended diagrams to assist with explanation in questions that don't have marks allocated for presentation or order or whatever it is they give marks for.)
I intend on writing in full sentences in most of my exams but I haven't a problem with scrawling down a few bullet points at the end of an answer if, God forbid, I run out of time. Better than nothing, right?