https://docs.magento.com/m2/ce/user_guide/catalog/category-best-practices.html

Best Practices for Product Categories

• Category Structure The structure of the categories in the main menu can impact customer experience and performance. As a best practice, it is usually best to identify one over-arching top-level category, and avoid having other categories with the same name. For example, rather than having multiple categories for “Women” organized under different departments, such as Clothing/Women, Shoes/Woman, Hats/Women, It can be more efficient to make the top-level parent category ”Women,” and then create subcategories as needed below. Be consistent with the category structure, and use the same approach for all product types in your catalog.

  Business Rules and Automation Consider the category structure and available attribute values when using business logic to show similar items on a catalog page, or to set up a personalized promotion, automated process, or search criteria. For example, if you were to specify “polo” as a parent category, the results might include mixed gender and age-inappropriate products. However, if you were to match a specific subcategory of polo shirts, the results would be more narrow and likely to appeal to a specific customer — especially when combined with other attribute values that target a specific customer. Consider the number of products that must be filtered through and retrieved when referencing a specific category path. The difference in results can be dramatic. Consider the different results returned by the following category paths: [Category: All Products/Shirts/Father’s Day/Polos/Sale] [Category Path: Men/Shirts/Polos] [Child Category: Polos] It’s important to clearly define categorical relationships such as parent category, sub category, category path, and any associated keywords and attributes such as availability, sale price, brand, size and color.