The problem IAM solves
IAM answers who in your company can access what, and who decided that. Without proper identity management, years of unused accounts, unreviewed permissions and shared passwords pile up, and nobody dares change them because nobody knows what breaks.
The most common concrete case is a departed employee whose account stays active, because accounts live in a dozen separate services and no single list exists. The second is a growing company where setting up each new hire takes days, because no step has been described.
Tidying access is part of a bigger picture. If you do not yet have an overview of the whole environment, start with IT management or order IT consulting.