Bumblebee-Project/bumblebeed — comment on commit b57231c322ae901936956b09eca6657c50dce0fb
File:  line 0
By Thulinma:

There is actually code for two behaviours, the default being "card on when daemon shuts down", but through an option this can be changed into "card off when daemon shuts down".
The reason "on" is the default, is because it may cause issues to turn off the card without "means" to turn it back on, for example when uninstalling bumblebee.