I've used them for 20 years. They're a permanent feature on my good road bike. I use the same normal road fit, no modification necessary. You sure don't want to mess up your road fit just to use aero bars now and then. That said, I use what's probably described as an endurance fit. My bar tops are 3 cm below my saddle. I used to have them 5.5 cm below and that worked fine too, but a fitter said my hip angle was too tight and raised me up a bit. The only difference I notice is that I can be fatter and still pedal hard tucked in the drops. Although the other thing the fitter did was tell me to get a different set of aerobars. They now are attached to the bottoms of my handlebars instead of the tops, I'm probably lower on the aerobars than I was. Whatever. I don't think that was wise, really. I use them much more to rest my hands and arms than to go faster.
All that said, take them off during the run-up to PBP if you're planning on riding it. Rule: never use them within 30' of a bike in front of you. You'd probably be OK being a little closer, but it spooks other riders. Get off them during hard or sharp cornering or descents with driveways..
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