>>10217404It's nice because having nearly all the sun's power be wasted does nothing for you and can even be thought of an ecological catastrophe. If you don't make something useful out of that starlight, it's gone to you forever. Modern applications include things like running inefficient processes to pull CO2 from the atmosphere and recombine it into hydrocarbons, solving air pollution and negating a lot of the need for better battery technology when you can just use fossil fuels indefinitely instead, or running industrial supercolliders to synthesize heavier elements instead of or in addition to mining them.
>>10220142You can build a partial Dyson that doesn't block the Earth. Alternatively, if you have the entire energy output of a star available, you can probably figure out a way to use it to heat/light the planet. Even if it's horrendously inefficient you're going to have a lot of energy to spare.
>>10222848>sphereYou only need Mercury if you just put modern solar collectors in orbit around the sun.
>>10223779>what is a laser 
