The content on a web page which can’t be seen without scrolling is called ‘below the fold’. This is a term that comes from the newspaper industry, and I’m sure we can all guess the connection.
It’s important. First impressions are everything, and for some visitors, it’s only what they see ‘above the fold’ (i.e. without scrolling) that makes them scroll down to see the rest.
There’s a little-known dimension in Google Analytics which allows a report to be created showing the actual browser window sizes of visitors. Try it, and there’ll probably be hundreds listed in recent months for your site. This means that what we see on our computer screens is unlikely to be what’s seen by more than a tiny proportion of our visitors.
Once we know the most common sizes being used by our visitors, we can take a look at what they’re seeing*. It might not be what we’d want.
*There are various Chrome extensions to resize windows to set dimensions, and some online tools too.