I'm curious to know because I was thinking that when people say this, I'm thinking they start editing the last chapter of their work to the first, and see if it all makes sense in the end. When I search on the Internet, it seems this is not what people mean by that. What I searched is that editing backwards is just reading paragraphs literally backwards, and one would have to still start on the first chapter. I don't understand this at all; it's counterproductive in my opinion. Which one do you think is more productive, and more beneficial for writers during their editing process? Reading each paragraph literally backwards, or starting on the last chapter to the first to see if one's story makes sense logically?
Literally reading it backwards is a technique used, particularly in editing, to pick up on any mistakes that might be present.
Particularly useful when self editing, as we are prone to "fill in the gaps" in work we are familiar with, whether it's there or not. Reading backwards means you are paying a lot more attention to what's actually written, causing any omissions or mistakes to be obvious. As per Amaedeus' comment: the reason this works is that when reading forward our brains have built in mechanisms to follow text, anticipate possible words and extract meaning as we go, and this can happen without any conscious effort at all, the mind paves over missing words, duplicated words (like two 'or' in a row, or a line ending in 'and' with the next line beginning with 'and'). It is related to getting meaning from speech, which is often broken, slurred, hard to hear, incomplete, etc, and we need to get the meaning quick. Reading backward defeats that automatic fixer-upper
It's also a useful technique to ensure that sentences, paragraphs etc flow correctly, as again it's forcing you to read it as something unfamiliar and concentrate harder than you normally would.
I'd also point out that it's just one tool in the toolbox, and should not be used in isolation.
Edit: Updated to include the comment by Amadeus