Errr.... I know that phone chargers draw some power even when the phone isn't charging, but surely it's orders of magnitude less than what they draw when the attached device is running at full capacity.
Not to mention how hot the damn things could get.
So it's going to cost me electricity and probably shorten the life of my phone - why would I sign up?
The app actually monitors the battery temperature (exposed on all Android phones) and throttles down when it exceeds a certain threshold.
The charging circuitry on some phones (not all) actually disengages the battery from the charging circuit path once 100% AC power is reached. In other words your phone's CPU runs off of AC power (and not via the battery) once 100% charge is reached.
Why you would sign up is where it gets interesting - the app works via a similar incentivization scheme as how bitcoin miners work - the more you run the app (mine) the likelier you stumble upon a valid proof of work, and you get rewarded by virtual currency.
Not to mention how hot the damn things could get.
So it's going to cost me electricity and probably shorten the life of my phone - why would I sign up?