Using mods and custom content is totally an individual's choice. I personally use it to spice up my game and create new and interesting scenarios with my sims. I also really enjoy building and furnishing homes for my Sims. I know I couldn't make them look the way I want without at least some custom content. However, there are valid reasons to not use mods or custom content. They can honestly be headaches and cause issues with the game, some people might not want to deal with it. You can also have to make sure to update objects and mods within the game when certain patches or packs come out.