1. Can I use images on this site without buying them?
Yes, provided this is only for personal use on a private profile, like FaceBook, MySpace and other community sites. The sites logo should still be visible on the image you post on your profile.
2. What more do I get by buying the image?
You get an image without a logo, that you can use according to the licence you purchase. Depending on your licence, the image will be of much higher quality, which means that you can display them in a bigger size without losing quality.