Microsoft Defender AV must audit executable files from running unless they meet a prevalence, age, or trusted list criterion.
This policy setting blocks executable files, such as .exe, .dll, or .scr, from launching. Thus, launching untrusted or unknown executable files can be risky, as it might not be initially clear if the files are malicious.
How this relates to the STIG checklist: STIG vs SCAP benchmark.