i think the major current emphasis on high effiency is due to the interest in low power set amps. you can experience some beautiful sounds with such. however one of the major potential practical down sides to the use of high effiency speakers is the demand of having a very quiet pre-amp and source - any residual humm or other noise, tube hiss for example, come to mind. i prefer lower effiency and higher power.
low efficiency speaker vs. high efficiency speaker?
What are the advantages and disadvantages of high efficiency speaker vs. low efficiency speaker? Does it mean that 93db efficient speaker will sound better than 86db?