If your organization conducts internal or external audits of management systems, or if you manage an audit program, then ISO 19011 and the ANSI version apply to you.
Anyone involved in audits or audit programs can use ISO 19011. More specifically, ISO 19011 is for people in charge of managing an audit program and evaluating individuals involved in the audit programs and audits. Anyone who has been tasked with improving an audit program will likely find ISO 19011:2018 of value.