I read or heard it somewhere that the original intent of Eccleston's "fireworks" type regeneration into Tennant was to depict him "expelling" the "Heart of the TARDIS" vortex energy which he absorbed from Rose to save her life. However, when Derek Jacobi regenerated into John Simm, the FX team applied a similar optical, thus implying the the violent release of energy is the norm for all TimeLords. When Tennant redirected the same golden flames towards his severed hand to stave off a regeneration, that pretty well cemented the visual as "the" standard. Afterwards, we got Teannant into Smith with the same effect as well as two regenerations with Melody pond/River Song.
If the production had stayed with the original plan of the "flaming" regeneration being a unique event, I wonder what effects subsequent regeneration sequences would have employed?