Or know if I'm still at work, so there's no rush cooking dinner... without bothering me if I'm still stuck in a meeting or something. Or close to home already, or not moving stuck in traffic, etc.
I love the extreme, sporadic examples such as these.
By taking my reasoning and extending it to extreme is not a good way to look at this. In that case, taking your argument, I can say the same thing about electricity or cellphone. I'm sure when those novelty first come into existence people are saying the same thing you are, but as they became more integral part of our lives eventually the argument subsided. (e.g., I can say the same about cellphone, what is the need of the cellphone? People can't just stick to landline, and wait to make phone calls when they get home, or get to a pay phone?)
Lets not compare the novelty implications of electricity to a "find your friend" app. Just... no...