I just got a new laptop and hadn't got around to installing uBlock yet. I'm comfortable saying the mainstream web is literally unusable without ad blocking. I watched the download notifications in the status bar iterate through dozens of ad servers, for 1-2 minutes, per page. I could barely scroll at all. I couldn't tell where the actual content was. All 3 columns full of ads. You have to hunt for isolated paragraphs of content.

The other glaring thing I noticed is the browser becomes a festering petri dish of promiscuous cookie-sharing. Every site obviously knows everything I'm doing on every other site.