Sometimes it can be a great help not to have to hold onto your phone while your waiting for the receiver to pick up. I'm thinking about calling customer service call centres and banks, or even when driving, although please remember holding a mobile phone while at the wheel is illegal in some countries.
What CallGuard offers is a simple vibrating function to alert you when the phone has been picked up at the other end. So make a call and then rest your mobile until you hear or see it vibrating. Then you can get on with talking. For normal telephone calls this can be a little annoying but, like I say, for calls when you know you might have to wait it can be extremely useful. Although unless you've got a good contract or someone else paying the bills you might not want to make those calls on your mobile. Never simple, is it?