Many games for Nintendo Svitch are available in retail as a plug-in / gamecard version and as a pure online version for Nintendo eShop. All the contents of the game are identical. The difference is that in the eShop version, the game loads on the internal memory of the switch or the micro SD card. In the Gamecard version, the main game is stored on the card, and only the patches and additional content are stored on the internal memory.
How much memory is occupied by Pokemon's Let's Go?
The game depends roughly on the download version 4.6 GB in the storage area. If you want to buy a digital version, make sure you have enough free space. Memory requirements are here, but they are still moderate.