Accessibility gets treated as a compliance chore bolted on at the end. Done that way it's expensive and half-hearted. Done from the start it's nearly free — and it makes the product better for everyone.
Most of the wins are structural, not cosmetic: semantic HTML, real focus management, labels tied to inputs, and colour contrast that clears WCAG AA. Get those right and you've handled the majority of issues before any assistive technology is involved.
Keyboard-first is the tell. If you can complete every core flow without touching the mouse — tabbing in a logical order, always seeing where focus is, escaping every modal — the experience holds up for screen readers and power users alike.
Bake it into the design system once. Accessible components — a proper dialog, a labelled field, a visible focus ring — mean every new screen inherits accessibility for free instead of re-litigating it per feature.
The benefits spill over: better contrast helps in sunlight, captions help in noisy rooms, clear focus helps everyone. Accessibility isn't charity for a few users — it's baseline quality for all of them.