Because it is difficult to accurately judge the approach angle at night there is often a tendency for both pilots to be heads up all the way down to over the threshold. While the well known 320 ft per mile for approach angle and five times the ground speed will give you the desired rate of descent, the last 500 feet is where real caution is required.
It becomes important for the PNF (and of course the PF) to keep a close eye for excessive rate of descent close in as that is where a too high or too low angle of approach suddenly becomes more obvious.
Because there is an understandable desire for both pilots to keep heads up as the aircraft closes with the runway, sink rates may go unseen and therefore un-checked at night on a black hole approach.
While a support call at 500 ft agl of airspeed, altitude and sink rate is a SOP for many operators be it day or night, things can go wrong very quickly below 500 ft.
To prevent excessive sink rate below 500 ft going unnoticed because of both pilots staring at the runway scene, some operators have an extra call by the PNF at 200 feet agl. This requirement forces the PNF to momentarily go heads down to read aloud the altitude, airspeed variance from Vref bug and sink rate. Example: "200 feet - Sink 900 - bug plus ten".
If clearly this support call suddenly reveals a potentially dangerous situation rapidly developing (for example, low thrust condition leading to high sink rate), there is enough height to conduct an immediate go-around allowing for spool up rate and current sink rate. There is a "survival" tendency for both pilots to be keenly looking through the windscreen at the runway lights especially in rain or mist and as stated earlier this means no one is monitoring the flight instruments or the thrust levels when close to the ground.
By having a SOP that forces one pilot to glance down at the instruments at 200 feet, the chances of not picking up a deteriorating situation are diminished. We used this SOP when operating 737's into black hole approaches into Pacific atoll airstrips at night with no glide slope guidance available.