A site can look fine and still be losing calls. Slow pages on a phone, titles Google ignores, missing schema, a Business Profile that doesn't match the site, pages Google never indexed. You'd never spot any of it just by visiting.
An audit finds those problems and ranks them by what they're costing you. The fixes that move rankings and calls come first. The nice-to-haves come last, or not at all.
It's the same set of checks behind every site I build, including the one that put Boss Bros RV at #1 on Google four days after launch. Fixing an existing site starts in the same place.