Irrespective of how interesting a particular thought or idea is, I would say that most of us find it quite challenging to hold it for long enough to derive any lasting benefit from it.
I believe that most books and articles are based on a single, core idea that is not necessarily explained in thousands of words (book form) for the purpose of clarification, but rather to engage the reader for long enough and enable him/her to understand it by way of immersion or saturation. ie. time spent thinking about it.
Core ideas and profound truths that are by their very nature always simple, must often be transmitted through books and other complex systems and techniques so that the complicated human mind has a chance at catching at least some of it. This is where writing comes in.
When I come across an interesting idea or question I feel like I just want to sit with it for hours and contemplate, see it to its conclusion. Writing it down definitely helps me to do this because it is a way of bringing the thought into the physical realm and anchoring it.
If it is written down I can develop it easier and look at it from different, previously unseen angles. It gives me the opportunity to scrutinize the thought and helps to develop focus, conviction and discernment.