A METADATA_NEVER_INDEX file is considered as a system file in a Mac OS platform. This file is a hidden file on a Mac OS computer and contains information that prevents indexing or listing of specific files, folders and directories. As the name implies, a METADATA_NEVER_INDEX file will prevent any indexing program to automatically index metadata information on a Mac OS computer.
There are certain programs in a Mac OS computer that incorporates advanced searching options on its features like the Apple Spotlight application. Though this application means no harm as it only intends to make searching, indexing and application launching faster, some users would choose not let any application automatically index a certain part of their folders, directories and partitions for various reasons. This can be achieved by modifying the Mac OS’ METADATA_NEVER_INDEX file and instruct a certain application to skip a specific folder or directory when searching and indexing files.
One very popular reason why some users don’t want indexing applications to search through a specific folder or directory is speed. Some users already know that if an application will browse through and index a folder that is rather big, it will take a lot of time for it to finish. And so, they would rather let the application skip the specific folder to save time. As of now, the only known program that can open a METADATA_NEVER_INDEX file is Apple Spotlight.