Ever since the invention of the wheel, people have been using it to make things go fast, and roller skates are no exception.  Boots, plates, wheels, and bearings have been modified and improved over the years to help them go faster.  Hence the invention of speed skates.

However speed isn't always enough.  Going round 'n' round as fast as you can sometimes gets boring for people, so some skaters like to add a little style to their speed.

Speed skates and jam skates fit both the desire to go fast and have a little fun at the same time.  The low-cut shoes help with cornering while going fast, but they also allow skaters to accomplish difficult tricks by allowing the ankles to move more freely.  Speed skates use unique wheels and bearings get skaters up to speed, but they also enable a skater to land jump-type moves and keep them moving along when truckin'.