Picric acid is not “everything”, it is a genuine high explosive - back in WWI it was commonly used as the explosive filling in artillery shells.
Picric acid was used as the primer for the propellant charge for some artillery rounds.
The ammonium salt was used in pyrotechnics. The burning rate of some of its mixtures is inversely proportional to pressure. As a column burns in a tube, it oscillates and produces the whistling sound heard in bottle rockets, etc. As the gas column gets longer, the tone drops in pitch, as it resonates like an organ pipe. Safer chemicals have been found that do the same thing now.
It is also used in some metallurgical etches.
It was used as a shell filler HE, but had a nasty habit of forming sensitive explosive compounds with many metals used in shells and fuzes. This produced embarrassment when they blew up in the muzzle, or in the back of an ammo truck.