There was some speculation here on the site yesterday that Warner Bros had chosen to put Lego City Undercover for Switch on a 8GB game cartridge instead of a 32 GB one, and then put the remaining 13 GB up as a mandatory download, in order to save money on cartridge costs. This was supported by images of the box art that said that internet connection was required and 13 GB of free space on the Switch's internal memory or on an SD card was needed. Warner Bros. has come out though and clarified that the information on the box was a mistake, and that the game does not require internet or 13 GB of free space. The game will have an optional smaller day 1 patch though.
http://www.ign.com/articles/2017/03/28/wb-comments-on-lego-city-undercover-switch-download