The SIC code does two jobs. For the public, it is an industry label: it tells a reader what line of business a registrant is in and lets companies be grouped with others in the same field. Inside the SEC, it is a routing key. According to the SEC's own code list, the Division of Corporation Finance uses a company's SIC code to decide which industry office reviews its filings — the list pairs each code with an office such as the Office of Technology, the Office of Life Sciences, the Office of Finance, the Office of Manufacturing, or the Office of Energy & Transportation. A metal mining company under SIC 1000, for instance, is reviewed by Energy & Transportation.
The list also includes codes that are not industries in the usual sense, such as 6770 for blank checks (reviewed by multiple offices), 8880 for American depositary receipts, and 8888 for foreign governments. Each company carries one code, so a diversified business is classified by a single line of work even if its revenue comes from several. That makes SIC a good first cut for building a peer group, but not a substitute for reading the company's segment disclosure in its 10-K.
GeminIQ uses the SIC code on the /comps page: it shows each peer's SIC code and description, and suggests same-industry peers by SIC code when you build a comparison set.