I've noticed that when I have decided to postpone writing about a topic it often ends up being a lot longer delay than I had originally thought. Sometimes those topics might even fade from my memory so much that when I read them from my topic ideas list I can anymore remember what I was thinking of writing back when I originally had the idea.
The most common reason for leaving a topic for later time is the need for additional research. Those ideas often come when I don't have the time to dig deeper into the topic. I also usually only resort to my list when I can't think of anything to write on the spot. Those times usually also are the times when I don't have the luxury of giving myself a bit more time to think about what to write. So obviously no time to do some additional reading either.