Logs are gitignored. It is recommended to always keep 'logErrors' => true configuration directive. In order to avoid writting into large log files, in case of too many errors, new files are generated daily. Each entry contains error type, level, file, line, message and more, like user agent or the referrer, for web errors. Even CLI errors are logged. After solving the cause of errors, you should delete logs. However is not recommended to delete the .keep file inside the log folder. These files are needed for Git purposes, in order to keep directories.
/workspace/admin/logs/ contains the Admin side errors.
/workspace/site/logs/ contains the Site side errors.
/workspace/api/logs/ contains the API side errors.
/workspace/cli/crons/logs/ contains the CLI crons errors.
/workspace/cli/scripts/logs/ contains the CLI scripts errors.