The Buccaneers signed running back D.J. Ware in attempt to add some depth to the running back position. It's clear that Tampa is going to place a lot of emphasis on the running game (call them old school), so the more ball carriers the merrier for the Bucs.
Here's some analysis from Bucs Nation:
With just 324 career rushing yards on 81 carries, Ware has not been a productive back as a runner -- but he was much more useful on passing downs. He has 37 career passes for 252 yards, with 27 of them coming last year. Current Bucs offensive coordinator Mike Sullivan should be familiar with Ware from his time with the Giants.
The addition of Ware brings the Bucs' running back total to four: Doug Martin, LeGarrette Blount and Michael Smith. Martin was recently named the starting running back over Blount, who was last year's starter.