Search Engines think you’re constantly making changes to your site as, chances are, that each time they visit the home page they find different content there.
You can use it to promote different products or content (of your own or of third parties as an affiliate) in rotation or at random.
You can use it to split test content when used in conjunction with click tracking software.
You can use a WordPress driven site as a niche directory site and use it to promote local businesses in your area for a fee.