The main difference between open source drivers and closed (proprietary) drivers is performance. The proprietary nVidia driver has much better 3D performance than the current driver for nVidia cards packaged with Fedora, called nouveau. However, keep in mind that nouveau is completely open and free, while the nVidia's proprietary driver is closed source. This means that sometimes a bug in the driver can't be fixed or an incompatibility cannot be resolved until nVidia decides to release an updated proprietary driver.