I make sure your site is able to display correctly on the latest systems and browsers (going back a few years).
If you want a mobile-friendly site, I make your site displays correctly on all of the most popular devices. Even if someone was to access your site from a really old computer or device, your site content will still display but probably not as well on newer computers or devices.
To learn more, see my blog post: Making a site cross-platform and cross-device