We regularly find ourselves close to a major airport and/or the flight path of incoming passenger jets - in order to assist ATC clearance to operate there, it's in our interest to make ourselves more conspicuous, especially against ground lighting where a helicopter at 1000-1500' will be camouflaged quite effetively from an inbound jet anywhere above our level.
As soon as I hear ATC inform an inbound of our presence, I'll light up everything (depending on weather conditions) to ease his workload and our mutual safety. HISLs are only an extension of an anti-collision light - the clue lies in the name!
