But you're focussing on people and healthy ones at that. Semantics matter a lot less there because you can style anything to look like anything else. But somebody with a screen reader literally needs semantics for accessibility. You set your page up as a table and their screen reader is going to iterate through it like a table.

And things like microformats are soft-semantics that allow your devices to explicitly know that "this thing here is an address", "that's a phone number you can click", and there's a whole bunch of formats for declaring embed data rather than making a service infer it from your actual content.

But if you just can't be bothered, do yourself and your users a favour. Use a framework (eg Bootstrap). It won't be perfect but it'll stop you using tables for layout and that's already a lot better. I can't believe it won't also look better.

This makes it not only usable by a web browser, but parsable by software. That includes, but is certainly not limited to, screen readers, assistive technologies, and search engines.

Consider an example where I use JavaScript to make <i> tags behave like links. I can make it “work”, but by doing so, I am disregarding—and breaking—a primary function of the language.