Microsoft Defender is a Windows built-in security solution that helps your user to be protected against phishing or malware websites and malicious applications and protects your user to download (potentially) malicious files.

Microsoft Defender SmartScreen provides a warning page against e.g., websites that might engage in phishing attacks or attempt to distribute malware through a socially engineered attack.

When Microsoft Defender SmartScreen is configured, you will have the following benefits:

• Anti-phishing and anti-malware support
• Reputation-based URL and app protection
• Fully integrated into Windows 10 and 11
• Management via Microsoft Intune
• Microsoft Defender SmartScreen is constantly learning
• Blocking URLs associated with potentially unwanted applications

Microsoft Defender SmartScreen checks the reputation of any website, application, or web-based app the first time it’s run. Microsoft Defender SmartScreen will check the digital signatures and some other factors against a Microsoft-maintained service. If an app or website has no reputation or is known to be malicious, Microsoft Defender SmartScreen will warn the user or block the app from running entirely.

So, Microsoft Defender SmartScreen is a security layer that needs to be implemented in my opinion to protect your users against the dark part of the internet.