Most ice makers and whole house humidifiers that I see have a saddle valve supplying the water. These are devices that allow for a very fast, cheap, do-it-yourself installation of a ¼” water supply line.
Saddle valves are installed by tightening a metal clamp on to a water pipe, then tightening down a needle valve until it pierces the water pipe. No cutting of pipes is required, no soldering, no special tools… simple. Very DIY. The needle just pokes a hole in the pipe, and it can even be done without even turning off the water (but I sure wouldn't recommend it). There has to be a catch, right?
There is. They leak, and saddle valves are prohibited by the Minnesota State Plumbing Code.
Most of them don’t leak, but they have a much higher chance of leaking than a properly installed water valve. If they do end up leaking, the repair will involve doing all the stuff that you’re supposed to be able to avoid – cutting, soldering, etc.
My advice is to not use saddle valves. If you’re installing an appliance that needs a ¼” water pipe, have a proper shutoff valve installed. It will certainly take more time, but you'll dramatically lower the chances of it leaking.
If you already have one in your house, try to leave it alone. Every time you operate the valve, you’re increasing your chances of creating a leak.