If you want peoples' eyeballs to not be dilated pretty widely, the modeling bulb light that strikes the face needs to be reasonably bright. If the modeling light has a variable brightness control, and the light is turned to a pretty low setting, if the lamp is a lowish output lamp to begin with, by the time the flash level drops to 1/4 power, the modeling light might not be "all that bright".
There are flash units with modeling lights with 250-Watt, 150-Watt, and 100-Watt quartz-halogen bulbs, and ones that use 100-,75-,60-,and even 35-Watt incandescent bulbs, of various actual output levels. Using flash units that have 250-Watt to 100-Watt, quart-halogen modeling lights in them makes focusing EASY, and positive, since the lights are bright. By the time I get to the lights I own that use three x 25-Watt incandescent lamps, focusing is much less sure...the light just is nowhere near as bright. Quartz puts off more light than incandescent in my experience.
There are also fairly bright LED modeling lamp setups, as well as power-saving LED modeling setups.
Sometimes you really WANT a really bright modeling light, and at the opposite extremes sometimes you want a low-powered one for use inside of a snoot, a small softbox, in a confined place, or to accurately represent a low-powered flash in a WYSIWYG type of way.
If you are running off of a battery or inverter, then low-Watt or very efficient LED modeling light systems might have a fairly real advantage.