Whilst times are normal, and the fire department are available, and the property afire is insured, I agree entirely that DIY firefighting beyond a single extinguisher is generally to be advised against.

IMHO there are exceptions to this general rule. For example I would consider use of multiple extinguishers on a fire from which escape is easy, near the exit door, ground floor only.
Also if a single extinguisher has LARGELY put out the fire in say upholstered furniture or bedding, then I would consider use of a second extinguisher to "make certain" and put out any glowing embers.

Other exceptions no doubt exist, but IN GENERAL if you can not put it out with one extinguisher, then yes run away.

The other condition justifying the use of multiple extinguishers would be fire in a TEOTWAWKI situation with no fire department to call and no insurance to replace the loss. Under such emergency conditions one might take risks to preserve valuable property such as food stores or vital equipment.