Let's say you're writing a research paper. You start with an introductory review paper that links to dozens of other sources. You want to evaluate whether these sources are relevant to your paper's topic, so you open them all in new tabs. Then they have other references, so you open those too. Over the course of a couple hours, you might have over 20 tabs you've opened. You then stop opening new tabs, and read them one at a time until you're done. A similar process can happen when doing research for an in-depth blog post, opinion article, or essay (except instead of starting with a review paper, you might start with one or more pages of Google search results).

Outside of work, you might sign up for several emailed newsletters with various links to articles per email. If you get about 20 newsletter emails, and you choose to read 10 of them with 2-3 interesting articles each, you end up with 20+ tabs to read through.

However, if you don't need to do that much research for a particular task (or you can get the information you need from just a few resources like a quality book), you may not encounter a need to open this many tabs.