No effect on security, and shouldn’t affect any connections that are already working, in fact, it may improve any issues you’re having. This is just for assigning addresses to anything that connects to your home network. Your Internet Service Provider only gives you one IP address, and your modem or router then assigns local IP addresses to anything you connect to your home network. If you look up the IP address on anything on your network you’ll see an address that looks something like 10.0.0.## or 198.162.0.## depending on the brand of your router or modem. These are addresses assigned by your router or modem, not by your ISP, and don’t work outside of your home network. If you have 2 devices trying to assign addresses it can cause problems, like the one I was having with iC Pro. It generally doesn’t affect intenet connection so you might not know it’s a problem until you try to connect between devices on your home network. The way to figure if you have it is to run IPCONFIG (on Windows) from a command prompt and if you see 2 IPv4 addresses with the above type address format (10.0.0.# or 198.162.0.#) then you have 2 and you just need to go into the settings for one of your router modems and disable NAT (Network Address Translation). Here’s my IPCONFIG after I fixed the problem showing just one local address. Initially I had two.
