What a site audit actually checks
Technical SEO splits into four buckets: crawlability (can Google reach your pages?), indexability (is Google allowed to store them?), performance (do they load fast enough?), and on-page (do they have the signals Google needs to rank them?). A good site audit hits all four.
The most common killers we find: noindex tags accidentally left on production, robots.txt blocking the wrong folder, JavaScript that hides content from crawlers, 301 redirect chains 4+ hops deep, and images served at 3000px when they're displayed at 600px. Each one alone can tank rankings.