So when I'm in an app like the phone dialer, text message, internet, or mail and I hit the home button what is the harm in doing so? Bad battery life? the phone becoming sluggish?
No harm, I do it all the time. No matter how the app is exited, the worst it will do is the same suspend it would do anyway. If you interrupt a process within the app, of course, you might mess something up within the app, but hitting the Home button isn't going to affect the phone.