Pokemon Sun and Moon has expanded in size and anyone who wants to download the digital copy is going to have to go and get a new larger SD card than the standard one that comes with the console.
The SD card that comes with the Nintendo 3DS is just 4GB and Pokemon Sun and Moon are large downloads. They will fit onto the card but this is going to leave very little room for any other game. If you wanted to download both Sun and Moon you won’t be able to fit them onto the standard SD card.
If you have played the demo Pokemon Sun and Moon you will also find that you cannot transfer data onto the bought game. So you are going to have go back to the start and begin playing all over again. The SD card just isn’t large enough to hold both the demo and the bought game.
Pokemon Omega Ruby and Alpha Sapphire were thought to be large at 1.8GB each but Pokemon Sun and Moon has beaten them.