Actually taking prednisone soon after an acute acoustic trauma is the right thing to do and may have saved that person from weeks/months/a lifetime of tinnitus, though the proper dose for acoustic trauma is usually 1mg per killogram of bodyweight, sometimes when you get into an acute trauma, it becomes an emergency and you don't have time to waste waiting days for a GP's appointment, especially if you do have prednisone at your disposal.
Does this mean you have to take prednisone everytime you are exposed to loud noises? Of course not, only do so when you notice severe symptoms after such an exposure (such as tinnitus or sudden hearing loss).
Does prednisone come with serious side effects? It does, however unless you use it chronically (over a month period) those don't last, and the withdrawal period is very short (just make sure you tapper it off if you use prednisone for over 2 weeks, and make sure you have someone around you when you do, as withdrawal symptoms do include depression), given the choice, I'd take that any day instead of a potential lifetime of hearing impairment(s).