You would do a dealer re-flash (primarily) for 2 reasons I can think of:
1) There is a factory service bulletin on the ECM that would fix some problem you have or is required by Dodge as a preventative measure. The dealers will flash your ECM a lot of times when you take the truck in for something completely unrelated; it's how they keep the ECM's current and protect themselves from warranty expense for known problems.
2) You bought your truck used and have no idea what the ECM really has on it.
- Mine: '09 GMC Sierra LTX ECSB 2WD - Deletes, 4" Exhaust, AEM CAI, DP LMM 2.6 Stg 1.5 Drag Turbo, BD Manifold, Diamond Eye Downpipe, All Season Diesel Performance EGR/Grid Heater delete, PPE Race Valve, Edge Insight, '08 Hummer Wheels, DSP5 - EFI Live tuning by Mark Broviak @ Danville Performance.