Yes it seems daft to use it when you just want to get your point over to someone with a phone call but for people who live long distance from family and friends it certainly ads something more to the conversation to see someone face to face so to speak that you wouldn't normally otherwise be able too.
It can have it's uses but weather or not it's useful to you is another matter,to me it definitely is as i travel quite a lot and it feels better to be able to see someone when your speaking to them then just a voice.
Also another point about the camera being of a low resolution and quality,that can actually be a good thing if someone doesn't have the best wi-fi connection,i'm not sure how ios and facetime on apple devices handles bandwidth but streaming less data over a lower resolution camera also has it's advantages,i'd rather have a lower quality cam that actually streams smoothly then one that is HD quality but yet stutters or cuts off every now and again.