My particular installation suffered intermittent no-start problems - sometimes only one of them would start. This called for an electrical bypass where the ballast gets power directly from the battery (like speaker amplifier installations), controlled by relays connected to the original headlight socket. (My starter has also been bypassed in this manner) Even if your HIDs don't suffer from power problems like mines, this is recommended so you can fire-up the bulbs even while the engine is not running (12.6V versus charging voltage 14 V).
Well, had I known any better before and gotten the electrical bypass done earlier last year, I would've run my Philips Halogens to their full potential. But now I ended up with Philips ballast and Philips HIDs, which illuminates road signs and lane markers all the better.
After all, even Sylvania SilverStar users (*wink* at White850Turbo) saw the difference.
Note, I used the original deflector in my stock headlight housing.