IT administrators use them to check if any users in their organization are using common or compromised passwords.
Security researchers and penetration testers use these lists to test the strength of login portals against known leaked credentials. 20K UHQ.txt
If you have downloaded a file with this name from an untrusted source, be cautious. These files are sometimes used as "binders" to distribute malware or "stealers" targeting the person who downloads them. IT administrators use them to check if any