Some airports with a selective routeing lighting system available often use "all greens" in normal vis (except at runway entry points) which makes life as lot easier for ATC. In low vis selective routeing is a CAA requirement at Cat III equipped airports. The "all green" mode of operation is fine as long as good lit information signage is available for unfamiliar pilots. LHR I understand is presently having it's lighting system changed to Alstom which should make it easier to use.