Revealing specific details about the operating system and the platform you are using to host your website can make it more vulnerable. While knowing that you’re using Windows/Linux as the operating system or IIS/Apache/nginx as your application server won’t make it less secure, it does help an attacker tailor his attack vector against your system. This type of vulnerability is detailed in the Owasp top 10: A5. Revealing information about your system may help an attacker.