I can't be any more clear. Whether you type it up, put it in a notebook, scribble it on a napkin, writing your ideas down has many benefits. I recently discovered this as I went through a spring cleaning of sorts through my computer's old files.
One, keeping a written record allows you to look back and see how you were thinking and articulating at a specific time period in your life. Its a personal benchmark for self-evaluation. For example, a lot of people feel they wrote a lot better in high school or college. Its possible. But many people just stopped writing when they began working. You can only observe patterns if you have something to look at. Whether it be ideas, short stories, poems, free-writing diatribes, it doesn't matter. It all becomes part of a personal portfolio of your work. To determine growth, you need reference points.
Two, as you gain experience and knowledge, the ridiculous can seem all the more plausible. As the saying goes, "one person's trash is another person's treasure". In so many ways, you are a different person year to year. What may not seem feasible at the time may be of great value to you later on. You can never tell in the moment so its worth writing it down!
Bottomline: In order to chart change and growth in your thought process (even after college!), you have to have some form of a written record. Blogging is one of the most efficient, least resource-intensive ways of accomplishing this. No matter how you go about it though, I guarantee you will find the experience rewarding.