Dynamic Disks allow you to have more partitions (they're referred to as "Volumes" in Dynamic Disks) than a Basic Disk allows, and they allow for Software RAID's of Hard Disks. As for a performance boost, from viewing the fun my friend had with his 11 Drives and random configurations, there is no boost. The risk is that if you choose to revert back to a Basic from a Dynamic, you lose all your data.