Before we can answer this we need to know what is port forwarding, how do they work and what is the purpose.
Port forwarding or port mapping is a technique to redirect a communication port request from one port/ip address to another port/ip address.
The port that need port forwarding usually will reside in internal network and the request will be handled by network gateway.
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The Purpose of Port Forwarding
By implementing port forwarding it will enable remote computers from the internet to connect to a specific computer in the internal network (LAN).
Is Port forwarding Safe?
It depends on of what services/devices you apply the port forwarding. If you apply it on game consoles like Xbox and Playstation then it is safe.
If you apply port forwarding in a CCTV or their DVR (Digital Video Recording) then there is a risk someone can access your CCTV and DVR. You can minimize the risk by put a good password on them.
Or if you port forwarding on a computer running windows 7, windows 8 or windows 10, make sure you turn on the firewall.