As you cook bacon fat renders out as the water evaporates. That evaporation carries some of the lipids along for the ride which will eventually condense somewhere. Another problem is the water tends to splatter when small bubbles burst which throws bacon grease in all directions. If youve ever cooked bacon on the stove nekkid, you quickly learn why this is not nearly as good of an idea as it sounds. The same thing happens in the oven. The fat that spatters onto the walls of the oven will burn and polymerize making it difficult to clean. So rendering most of the fat through souls vide greatly reduces, but does not eliminate those issues.
As far as the eggs go, yes you can cook scrambled eggs from start to finish in 3-4 minutes, but many people prefer not to. Egg proteins denature differently at different temperatures. If you think of a hard boiled egg, the whites are rubbery while the yolks are dry and chalky. The same thing can happen with scrambled eggs. Some people prefer them this way, and just about every restaurant in America cooks them this way. Another way to cook them is slower without allowing the temperature of the eggs to exceed about 185F. The result is softer curds and a creamier texture. By using sous vide to pre-cook them to 147F, the thermal journey to done is much shorter than from refrigerator temps of around 40F. So its an easier and faster way to control the temperature to achieve the same result.