installing Late Night

why do late night has a different way to install? like i have to uninstall the whole the sims 3 + expansion then i can install late night. i read this from the installation guide after extracting the rar.

but i don't want to do so. it's going to be a long journey since my laptop is not that good for games and it will take hours. 

and why does the size of late night is big?

and is there another way that i can install late night without uninstalling the base game and other expansion? thank you.

You dont have to uninstall anything. Please read https://games4theworld.forumotion.com/t1171-must-read-how-to-install-the-sims-3-correctly-must-read