I know I posted another question regarding taxonomy and maybe this question is similar. I'm wondering if people can give me their opinion on the benefits of custom post types. The reason I ask is because I'm arguing with someone who suggests that just using tags is "easier" for the user instead of having fields to fill in. In other words, they're arguing that it's easier for the person updating Wordpress to use tags instead of filling out custom fields within custom post types.
This may be true (not likely) but I'd like to better understand all the virtues of custom post types and fields. I need to better explain it to someone.
The main benefit for me is that you can use custom post-types to cleanly separate your casual posts from content with special data, e.g. photo galleries, events, product items, complex tabular data content, and so forth. It becomes particularly powerful when you combine custom post-types with pre-defined custom fields, as you said, that are exclusively assigned to a specific post-type.