If you're looking to go all-digital with the Nintendo Switch, you're going to need some external memory. While physical cartridges will not require any installation to the system. Games bought in the Nintendo eShop will require your Nintendo Switch to allocate some of its 32gb internal memory for the game. Here's a list of some of the digital download sizes for games set to release on the system. 

• The Legend of Zelda: Breath of the Wild - 13.4 GB
• Mario Kart 8 Deluxe - 7 GB 
• Snipperclips: Cut it Out, Together! - 1.60 GB
• Disgaea 5 - 5.92 GB
• Puyo Puyo Tetris - 1.09 GB
• I Am Setsuna - 1.40 GB
• Dragon Quest Heroes I·II - 32 GB
• Nobunaga’s Ambition - 5 GB 

As you can see Zelda comes in at about half of that size, and Dragon Quest Heroes I and II will take up the entire console memory. Personally, I'm just going to whip my DS game case out of retirement so I have a place to keep my physical library on the go. If you are dead set on digital, you're going to want to factor in a 128 GB SD card to add to your console. Those are only about $40, mind you, but it should be enough for a few games should you decide you absolutely need a digital library. 

Source: IGN