Originally Posted by tjspiel

That's exactly right. With a drop bar riding on the hoods puts your hands a few inches in front of the handlebar clamp. On a flat bar your hands are about even with the clamp or slightly behind it (since flat bars are often swept back at least a little).

So when converting to drops, you'll typically need a shorter stem in order to compensate. This might change the handling of the bike in unpleasant ways. On my bike it seemed to work out fine but I doubt a professional fitter would find my setup to be very ideal.

edit: getting the stem right was one of the more challenging parts of the conversion. Road bars have a different diameter than flat bars. This means you need a stem designed for road bikes. Short road stems with a lot of rise do exist but aren't common. To get the bars in the right position you might even need an extension for the steerer.