I learned this from another customer of our builde near Regents Park.
They have a neighbour just built with ******* Home, and high up under the eaves outside of Main bedroom on first floor, there was a sensor light installed. The idea was to put it high up there so that the area it can detect movements (and turn on the light) will be larger.
After they moved in, and electricity connected, they found that it's giving too many false alarms as the sensor picks up lots of activities from the neighbour's back yard as well. They tried to adjust the sensor and guess what, they can't reach it any more as it's too high and they have to pay someone with really long ladder just to adjust the sensor's covering angle. Of course the other option is to turn it off, but since you already paid the money for that, why border switching it off?
The lesson/tip is, if you are planning for external lights, make sure it's within reachable height.