You can theoretically add any type of content in WordPress posts and sort them with categories and tags, but sometimes this is not ideal.
Below are some signs that indicate you should probably consider creating a custom post type, custom taxonomy, or maybe both working together:
Some content you are posting just doesn’t look and feel like a post. For example, our blogging coupons page.
Your content doesn’t need to be part of a chronological series of entries. For example, our WordPress glossary section.
Categories and tags won’t help you group and sort that particular content. For example, the specific sections in our coupons area.
You need additional fields to enter more information with your content.
It cannot be part of your pages. For example, our Blueprint page is simply a page with several subpages.
You need to display that particular content differently than posts or pages.