Is the brake wear sensor a good indicator of time to change brake pad?

[willos]

I have a question concerning whether the brake light warning system is a good indicator of time to change the pads or is it just a conservative measure?

Background: I change my pads (first time) recently in anticipation to avoid cutting the wear sensors. The old pad is worn down to the sensor hole so it is quite close to the point where the sensor will be earthed. But I noticed that there is still a lot of pad left (30%?). This leads me to wonder whether the sensor system is too conservative? Would I get much more out of my pads (without compromising brake quality) if I ditch the sensors and monitor the pad level manually?

[RFM]

The sensor is a good indicator if the pads are installed with new rotors at the same time, used rotors with, for example a outer edge of 2mm, will cut of the sensor 2mm earlier and it looks like the pads have only used 3/4 or less of there friction material.