I glow when ever I remember to hot or cold. The less raw fuel that goes in my engine the better. But when the engine is hot it will starts without them but I do haveto crank the engine longer.
It all depends on the condition of your engine,starting system and fuel injection system. With some cars you may need to glow most of the time or your risk not starting at all even in warm weather.
One of the members commented that using the glow plugs reduces the load on the starter/battery.
In the end it is your choice. Also about a month ago there was a thread asking the same question.

__________________
84 300D, 82 Volvo 244Gl Diesel