Some people theorize that any residual CO2 that might be in solution (or, less likely, some newly created from the priming sugar) will rise to the surface and push out the O2 from the top of the bottle. Letting the caps sit loose will allow the O2 to escape, as CO2 is heavier and will sit lower in it. It's a strong theory, and probably has some merit.
I typically fill all the bottles and leave them capped but unsealed until I'm finished filling... until I hit the 2 - 3 year mark with bottles, I rarely notice any off flavors, and that's probably not the O2. Many people fill and cap immediately. I avoid this only because it takes so much longer.
Make beer, not bombs.
(...and not bottle bombs either.)
Primary Fermentor - *empty*
Primary Fermentor -
Secondary - Mystery IPA
Bottle Conditioning -
Keg Conditioning -
Draft: - Apfelwein, Belgian-style Dubbel w/ Grains of Paradise
Bottles:(and still in stock): FIRST AG - (I)IPA 4.1.07, PK's Warm Spring Marzen, Summer Cerveza -BANG, PK's Winter Spice II, Espresso Stout, Indiana Pale Ale, PK's Chocolate Bitter II, Porterfield Porter, and New Year's 2006 remnants.