My planner philosophy is pretty simple.
Write down things that need doing. Keep it easy to read. Do the things that need doing.
I don't have much time or valuable planner space (like the weekly pages) to waste on decorating.
There are two exceptions.
1. DECORATE PERMANENT PAGES
Pages like tabs, dashboards, and yearly recurring future pages will be used again and again, so those are great places to spend time decorating.
2. DOODLE ON PAST DAYS
TIP: Use a highlighter so that material is still easy to read.
In the above picture, I did just that! As an added bonus, I get to easily find today's planner entry.