Flare or not? Depends on what you want/need...

NOT - I'm winter camping and want a nice cozy fire to sit by.

Definitely - I've fallen through the ice, gotten soaked, the only fuel at hand is snow covered and icy, and I need a fire before hypothermia stops me from doing anything. I don't care about odor, carcinogenic chemicals, etc. I just need fire fast.

As a military mountain survival instructor, I wasn't carrying a flare to light the fire to melt my C-ration (only peaches and applesauce were edible frozen). I was carrying it for a dire emergency.

For non-emergencies I've relied on strike anywhere matches, carried in a match safe, and lots of tender (usually pine needles) for over 40 years.

As far as using a road flare to start a fire, well, one just needs to watch their local fire department light a training fire...