It supports company’s business. It’s does not give any competitive advantage, contrary to core subdomain.
Supporting subdomain is simple. Mostly resembles CRUD interfaces, ETL operations. This makes it the best candidate for outsourcing.
Strategically the company would prefer its supporting subdomains to be generic, ready-made solutions. Because it would mean that they could save on designing and implementing their own solutions.
How to Identify in the Legacy code (Brownfield project)
After identifying Core and Generic subdomains, they are what’s left off. They can’t be replaced with ready-made solution, but at the same time they don’t provide a competitive advantage.