A lot of people debate about using categories or tags in WordPress. First of all, we need to clear the confusion between what one or the other actually is.
If you want to use pro language, in WordPress terms both the tags and the categories are called taxonomies, and the purpose of both categories and tags is to make the usability of your website better. More precisely, it helps users who get on your website find their way easier, and find the content they want easier.
Categories are more general than tags. They offer a broad description of what certain posts are about, and they make it easier for your users to locate a certain content type.
Tags, on the other hand, are more specific. Unlike categories, which are used to offer a broad description of certain posts, tags are used as a more precise description of said posts.
Know that categories are something that must exist on your website, and you must put your posts into a category, but tags are option. Both have a purpose, and neither one is better than the other. Both should be used together to create a more functional website. They have a very important role on the website, and neither one should be neglected. If you fail to utilize one or the other, you will leave yourself at a disadvantage.
People often wonder and ask what the best number of categories on a website is. There is really no true answer to that question, because the number of categories depends primarily on your website. If you have a simple website, or blog, with little variety in content, you won’t need too many categories. If, however, your website is more complex than that, and you have a wide variety of content on it,than you may need it.
Another commonly thrown around question is whether there is a limit to the number of tags you can use for a specific post. Nope, there is not a technical limit, but you should obviously not use a thousand tags for each post. Tags are used to make your website more interconnected, and to allow your users to find content more easily. If you put a hundred tags on every post, you will juts make things complicated, and the defeat the purpose of the tags and why you used them in the first place. Usually, what would be suggested to you is not to use more than 10 tags for every post. That is, if you have to use more than 10 tags because of some reason, then you can do it, but you should stay away from using too many tags.
Both tags and categories are important. Categories are something that you must use, and tags are optional, but both should be used on your website. They work in a way that they increase the usability of your website, as said before, and help users find content more easily. They generally make for a better website, and we all want our websites to grow.