I have only seen this on 737 series airplanes. I was on a maintenance course and the I was told it was a way to have the aircraft noticed by possible conflicts on landing and take off, birds, other aircraft ect..
It had been shown that the steady beams were not very visible during the day and the solid beams were something that other aviators are used to and it can go unoticed due to constant exposure.
I was also told that the intermittent lights did not affect the view of the pilots as they only go off momentarily then on again.
Having said that I have never seen any other types fitted with the flashing or rotating light cycle.
The flashing you see is basically a rotation from on to off of the inboard and outboard landing lights as well as the taxi and turn off lights.
Hope this helps.