1 - they keep your feet dry through quick streams dunkings, light rain, and careful snow travel.
2 - once water gets in (usually through the top), they do not dry as quickly as their non-waterproof counterparts.
That is the give and take of waterproof hiking shoes, they keep your feet more dry in certain applications, but keep them more wet in others. Read our How To Choose Hiking Shoes to read more details on this topic. Or a quick general summary: we prefer waterproof shoes for snow situations and otherwise prefer non-waterproof.
The waterproof shoes are $20 more expensive than the non-waterproof Ventilators. That is not going to break the bank, but the Ventilators are an amazing deal in our opinion while the Moab Waterproofs are just a good deal.The final difference between Ventilator and Waterproof: color. The Ventilator comes in more colors but we generally prefer the more feminine accents on the waterproof shoes. But neither is our favorite hiking shoe in the looks department.