Should i disallow incoming traffic even there is no service to process it?

Hello,

1)
If on a Linux server is running only two publicly available services, lets say an Apache web server and a SSH server, is it still important for denial of service attacks mitigation to still disallow all traffic that does not match these two services even there are no other public facing services? Or it does not matter? Can you shortly explain why it matter or why not?

2)
Maybe in my layman point of view I am forgetting that Linux has more services/apps which can be affected by...

Should i disallow incoming traffic even there is no service to process it? WordPress ...