Without the security, you will have people piggy-backing onto your connection which isn't that bad in itself but it also gives the people with the know-how access directly into your computer. It may never happen but if a hacker wants to get in and plant a trojan, keylogger or other little nasty, not being secure makes it terribly easy for them. A lot of people think there isn't anything they worry about in their computers but then the hackers can do things from your computer and it looks like YOU are the one doing it.