Because you got answer, here a extra cherry just to think about
- there is already easy access route to categories
- for mobiles putting all categories to the sidebar makes it really crowded (unless you have type max 5 categories)
- mobile users must open the sidebar to see categories and then it hides other content totally
- categories of the sidebar is something that users can customize. Then hiding all not-so-important ones gives much more pain than letting users decide what categories are important to them