When reviewing a site with CSS disabled, "sea of white" appears: is this a real accessibility issue?

Hi all,

 

When I was trained to do web accessibility testing, one thing I was directed
to do was to disable CSS and review the page to observe how it linearizes.
But I was also informed that if large white spaces  ("seas of white")
appeared in this view, that was an accessibility failure because it impacted
users who needed this view to compensate for low vision. I have more or less
accepted this on faith, but wanted to solicit your advice on whether this
assumption is correct. I find quite often that seas of white appear because
social media features, which in an CSS-enabled display are quite small, in
fact import a page from the social media, and the effect is to render what
would otherwise be "invisible" content" into white space in CSS-disabled
view. 

 

Andy Keyworth