bluetooth headsets, what that all about?

I know that they are hardly a new thing and I am a bit surprised to be writing about them. but I had to. yesterday I was out in my nearest city having a look around bit of shopping playing on the mac's in the mac shop (wondering how long a macbook air would last in my house).

when having sat down for a nice coffee I could help noticing the bluetooth headset that one middle aged lady had on, it was the black version of the one above. I tried to get a picture but was too worried that her (much larger than me) friend/coffee partner/husband might get cross. then I started to think and look more. quite a few people had bluetooth headsets on. not the average people you would think of delivery van men/women sales reps, I know that sounds pejorative and I apologise for that but I am sure you know what I mean.

what do these all these people need them for, how important are the calls they might miss? I have my phone with me most of the time but tend to turn it off when I am sitting down for a coffee, in fact its on silent msot of the time. I know in the scheme of things what I am saying is really not that important but I had to say it somewhere.