Here is just one of a couple of scenarios where this could come up. Let's say you add a plugin on your development server, which requires a wordpress page to do its magic. There are a couple of problems.
- There is no easy way to move the page over to production. The pages and posts are intermingled.
- Event if you do move it over, there is no guarantee that the pages ID will be the same, since likely new content was created on production in the interim. Most plugins that operate this way, store a page ID.