Crawl spaces with significant amounts of crawl space moisture are almost always going to end up with mold and mildew. Mold and mildew thrive in areas with significant amounts of moisture; any time your crawl space moisture gets up above about 65%, you can pretty much guarantee you’re going to end up with mold and mildew in the crawl space.
Mold and mildew can cause anything from serious allergic reactions to general respiratory concerns, and it’s also a great source of food for many insects. In general, it’s something you want to get rid of. If you can get rid of it through something as simple as crawl space encapsulation, you should definitely consider investing in it.