Markup you can actually read
HTML that arrives from a build step or a CMS is often one long line. Formatting re-indents each tag by how deeply it is nested, so the document's structure — which elements sit inside which — becomes obvious. That makes it far quicker to find the block you need to change.
Honest indentation
This formatter indents literally rather than rebuilding a corrected tree. If a tag is never closed, the indentation will drift — which is a feature: it shows you the mistake instead of hiding it. All of it happens on your device, so nothing you paste leaves the page.