With the amount of times ad networks like googles have spread malware etc it's a basic internet security practice these days.

Also a great practice if you do any amount of browsing on mobile as it’s practically impossible to read any mobile website through all the stupid ads. Just today I was trying to read an article on my phone in a browser without ubo and was basically blocked from doing so by a full screen video ad that kept popping up on its own even after dismissing it