I agree with tomtom here, they're not essential for several reasons. (best task I've found for one was searching my dark rucksack inside)
When you need one it would probably be at night, where it's dark, but you will probably have a fire going already and this one close to your shelter.
Setting up camp should be done before sundown, I have tried to set up a bivouac when it was almost totally dark, with just a little tiny torch (maglite solitaire) and it wasn't funny as it resulted in wet gear (and we had 4 days to go). So even though they provide light, it's not as good as daylight and human vision. They also ruin nightvision, though there is a trick to avoid this.
But... You might just wanna take a look
here. I haven't tried it though, but it's worth a read. I have a Maglite Solitaire and i'm not very pleased. The light is poor and the range also. The mini is much better and more powerful. But I know a lot in here dislike Maglites.
My thoughts.