I am a firm believer in the value of sketchbooks. Some of the greatest minds in history from Leonardo DaVinci to Albert Einstein to JK Rowling have employed sketching as a methodology for observing, understanding and reflecting upon the world.
When we help our students cultivate a practice of visual journaling--utilizing images, text and artistic experimentations--we are giving them access to a space for creative expression and deep learning. Further, we do so in a way that is unencumbered by highly structured note-taking schemas that can limit students' attachment and internalization of the material they are recording.
This is not to say that visual arts teachers should not give prompts for students to explore within their visual journals. The trick is finding a balance between crafting prompts that lead somewhere--learning a new art technique, exploring big ideas for an upcoming artwork, doing and responding to research--while at the same time are open-ended enough for students to take ownership of them and have an authentic response.
If you are looking for inspiration for how to implement visual journaling in your classroom, I would recommend checking out the Journal Fodder Junkies, David Modler and Eric Scott. Both Modler and Scott are arts educators and accomplished artists who advocate for the use of visual journaling as an artistic and educational pursuit. Their books The Journal Junkies Workshop: Visual Ammunition for the Art Addict and Journal Fodder 365: Daily Doses of Inspiration for the Art Addict are full of explorations for visual journaling--from experiments with media to prompts that push critical thinking.