A pioneer friend of mine told me that they were told in Pioneer School that the rest of the congregation looks up to them as good examples. So, with their busy door-knocking schedules they may not always have time to prepare for the meetings. When this happens, they should at least take a highlighter and underline random sentences. It only takes a few seconds, but can prevent stumbling the "weaker ones" which could make them bloodguilty.
It's all about appearances. We had an elder that would have every single sentence highlighted (in different colours which represented something to him I guess). He would put that magazine in a leather binder and hold it up high in front of him during the meeting for everyone behind to get a good look at his thorough "studying". He actually thought he was "being a good example".