Downloading games from Nintendo eShop while being in sleep mode saves time.
You can use an USB drive, microSD card or playing it straight off the hard disc of your console - either in docked mode with a TV connection or undocked wireless without any TV connection. You also need a nintendo account with access to the eshop store and enough money to buy your desired game. The first time you open the Nintendo eShop app on your Nintendo Switch while being in sleep mode, it will automatically download all required files. Keep in mind, that downloading games from nintendo eshop is still not possible while being offline.
It would be perfect, if there are no other background tasks running on your Nintendo Switch. Does Nintendo Switch download in sleep mode? - Gaming is magic Sleep mode is the best way to download games from Nintendo eShop.