Kegging packages finished beer into a keg (most commonly a Cornelius or "corny" keg among homebrewers, or a ball-lock/pin-lock equivalent) and carbonates it with CO2 under pressure directly, rather than relying on residual yeast fermenting priming sugar the way bottle conditioning does.
Speed and control are the real trade-offs against bottling
A kegged batch can reach drinkable carbonation in as little as a day or two with a force-carbonation method, against bottle conditioning's typical one-to-several-week wait — and because carbonation is set directly by regulator pressure rather than calculated in advance and locked in at packaging, a kegged beer can be adjusted after the fact if the first pour comes out flatter or fizzier than intended, something a bottled batch can't do without repackaging entirely.
Equipment cost is the honest trade-off
Kegging requires real upfront investment — kegs themselves, a CO2 tank and regulator, gas and liquid lines, and typically refrigerated storage to serve from — that bottle conditioning simply doesn't need beyond bottles, caps, and a capper. Most homebrewers who keg do so after bottling enough batches to decide the speed and convenience is worth the equipment cost, rather than starting there on day one, and many keep a bottling setup around for gifting or competition entries even after switching.