Unlike most earthbound fires, the spaceship captains can order the air to be evacuated from the effected sections, if not in an emergency to be opened directly to vacuum, or the usual practice of removing the air just before entering combat.
Explosions and radiation would seem to be the predominant threat against a prepared crew.
the problem with venting is having crew in Vacc-suits when the fire starts. If it takes say as little as five minutes to get a suit on, sealed , and activated they may be working in a toxic soup of combustion by products, and near combustion temperatures.
even with a soft suit, or emergency suit the time to unpack the suit, get into it, and get your mask on is not exactly a speedy process. fire retardant undergarments, and face masks will protect the crewmen for a few minutes but in blinding smoke, intense heat, and a very high level of stress even trained crews have a hell of a time getting into protective gear.
if crew are injured they would have to be helped into rescue balls, or some other form of shelter from vacuum. this mean you have a lot of time for fire to spread.and with a high intensity fire a minute is a very long time to wait.
once the fire is out, you have to wait for exposed surfaces to cool, and the source of initial ignition to cool down to point where it wont rekindle the second fresh o2 is introduced.
Ignition points could also be hidden, a fire could travel along utility safts, wiring conduits, and behind wall panels for quite some time before the crew even knew their was a fire. without a very well designed detection system the first sign of a fire could be a wall of flames and smoke suddenly erupting from a panel opened by a crewman t check and see what is causing a fault larm int h wiring or piping systems in a service crawlway.
"Hey where ya going Harry?"
"The number three buss is acting up again, I need to go fix it...give me hand with this Ha..whoooossssshhhhh Whompfffffffff..........aiiiieeeee aieeee urrrrrrrrkkkkk!!!!"