Yes, 1) - in case the onboard RAM gets malfunctioning. And you may not want upgrade it, but to just leave in the board and make BIOS use only the soldered RAM.

Resoldering a couple of resistors on the board seems like not a big deal to make BIOS forget the soldered RAM. As I am planning to buy a laptop with partially soldered RAM, I want to ensure the possibility of dealing with it successfully.