So something as simple as giving someone access to your wifi network (or them gaining access), would effectively grant them access to every device on your network. That can’t be good, especially if you have your alarm system coupled to it?
Guess it goes a little like this: Did you like playing toktokkie as a kid? I really do not want my neighbour’s kids to, for example, decide it is a fun idea to turn off my pool pump every time I turn it on…
I do run a guest network myself, but this isn’t fool proof.