A software policy makes a powerful addition to Microsoft Windows' malware protection.
In particular, it is more effective against ransomware than traditional approaches to security.
If you know about the Linux 'execute permission' bit then you'll understand what this is for. The mode of operation is somewhat different in that execute permission is granted to folders and subfolders rather than individual files, but the intention is the same, to stop undesirable or unknown software from launching unless you OK it.
Additionally, it is possible to specify that certain executables (typically browsers and email clients) are run with reduced rights. This is a valuable damage-limitation measure against browser plugin vulns, etc.
The protection can be turned off without a reboot whilst installing legitimate software, and will automatically reactivate after a specified time