Straight from their website, "Minimalism can bring great elegance, beauty, and usability to a website...". This is very true. White space is just as powerful if not more powerful than space that has been filled. Not many people outside the design world would agree, but that's because they don't know what they are talking about! White space is essential for good design and usually clients want to just fill up every space with something. DO NOT, I repeat, DO NOT let them do this. It's a bad idea. Minimal Exhibit showcases this idea with all the websites they have compiled.
Another great thing about this site is that designers can submit their own sites to the site and visitors to the site will be able to actually visit that site, so you can get the full gist of the site, rather than just seeing a picture of it. This is great for the designers/owners of the site, because in turn they are getting exposure to their site.