En An Intro To Screen Reader Testing for Sighted Developers se explica:
Why You Should Know How a Screen Reader Works If You Are Sighted
With a near perfect (either corrected or not) vision, you might never feel the need to use a screen reader when browsing the internet. So obviously, there's no need for you to understand how screen readers work or how to use one, is there?
As a person who develops sites and applications on the web, it might already be second nature to you to make sure that the websites that you're building work as expected for your users. Checking that a web app runs fine for different user flows or that its design looks as expected across a range of browsers is crucial and might already be part of your daily routine at work when delivering a feature. Now imagine how difficult it would be to deliver a bug fix for a misaligned navigation bar on a site without having a single glance at your screen. The visual check turns out to be important to confirm that your fix for this styling bug addresses the issue, is functional and works fine in different browsers.
Thinking about bugs that concern accessibility, is there any valid reason why a functional check would not be needed to address issues and provide valid bug fixes? Manually testing the accessibility of the websites you're building is insightful and can be the most valuable confirmation that the patches you deliver to improve its usability actually work just as expected.
To be able to manually test websites for accessibility concerns, getting familiar with the basics of screen readers is essential to understand how users of assistive technology experience your site.