What can go wrong on a branded SERP
An undefended branded SERP can host any combination of: competitor ads bidding on your brand, third-party review aggregators (Trustpilot, G2, Glassdoor) ranking above you, comparison pages from competitor blogs ("Brand X vs Us"), negative review forum threads, AI Overviews that summarize from unflattering third parties, and old social profiles you forgot existed.
Each of those elements either dilutes the conversion or costs the deal. A user who sees a competitor ad above your organic result has a meaningful chance of clicking it. A user who sees a Glassdoor 2.4-star above your About page has a meaningful chance of dropping the conversation entirely.