Not all modelling lights turn off when the studio strobe is fired...Buff designs its flashes that way as a visible indicator of the flash being ready to fire the next shot, but many photographers find this to be distracting (it leaves you in the dark if there are no other ambient lights in the room!). Most pro studio gear does not bother with this annoyance or 'feature'...most brands have the modelling light always on when modelling light is turned on, always off if turned off.
The modelling light lets the photographer SEE how the lighting falls on the subject without taking any shots, it is not intended to be a constant source for shooting with the strobe because the modelling light color temperature is so different from strobe flash lamp (close to daylight WB). You can use it as a constant light source (multiple studio strobes, all as constant sources) but Buff modelling lights are not bright enough at 150w, and even full blown studio flash are dimmer (at 250w) than true professional photoflood bulbs.