The free themes in the .org repo are the ONLY themes you should use! Commercial themes are essentially a scam on people who don’t know what they are doing.
Here are the use cases:
If you are building a single business
You want to use a child theme of a free theme in the repo. You had better have an extremly good reason not to use a theme built from Automattic [the company that makes WordPRress]. With
Every WordPress install comes with
twentysixteen
twentyseventeen
twentynineteen
Additionally, the same parent company publishes:
StoreFront
Underscores
Insist that all design be HARD CODED in the child theme
If you are an agency, and plan on building many themes for clients