Comment by d-us-vb

The real problem is with trust and encroachment. I think a lot of people that spend a fair amount of time on their computers start to feel like their OS is their home and they go on excursions through apps. Previously, ads were limited to apps you had to go to yourself. Ads showing up as wallpaper in your house would be unsettling, and it reveals that your homeownership was illusory from the start: you never really controlled anything.

Yes, you can use cleanup software to fix the symptoms, but that's not the real issue here.

Edit: further research revealed my original first point was a false assumption.