Here are some of the main objectives of concept art.
1. The process is an investment in ideation and exploration, resulting in your first looks at what the product could be.
2. It is also used by the production team to create the final asset. Each department, stage of development or industry type has different needs. Some need to create something from ground up; others are trying to fit new assets to existing styles. Assets may require callouts, technical drawings, Turn around sheets, color boards, material breakdowns, etc., which all qualify as concept art.
3. Finally, it can help predict and identify a wide array of potential design and technical problems early on.
The end result isn't necessarily a beautiful illustration but more something that assists in the production.