Why are high efficiency speakers preferred for low volume listening?

@audiokinesis  , thank you for oversimplifying.  That helps.  

@james633  , thank you for the feedback on this.  I think I am getting the picture.  High efficiency doesn't take as much power to move and at lower levels not as much power is being provided to the speaker as at higher levels.  

@elliottbnewcombjr  , I am actually not the one with the KEFs, that was @zlone  .  I am trying out a pair of Revel M126Be's.  I like them so far, but after reading posts here in the speaker forum, I am questioning myself as to whether a higher sensitivity speaker would have been a better coice in the small room I listen in.  My amp does not seem (to me) to be straining in 50 wpc.  I know your opinion of triode versus ultralinear, and today I put another 5.5+ hours on them, and for the last couple of hours I went to 100 wpc ultralinear and I felt that female vocals took on a bit of an edge in that mode.  I guess the final proof (or close to final) will come in about 20 more listening hours when I follow @soix  's advice and hook up my old speakers and see how I feel about the difference.  As always, I appreciate your feedback.  It is always welcome. 

I've never observed any correlation between high efficiency speaker and improved performance at low levels. Rather, (again, IME) the most important characteristics to enjoyable listening at low volumes are resolution of low level detail and microdynamic shading (as opposed to macrodynamics).  These can be found, to varying degrees, in both higher and lower efficiency speakers.

With that said, at the extreme, I have noted as a characteristic that very low efficiency speakers (e.g., <84 db/W/m) tend not to be very good at preserving microdynamics.

I came across this article a few years ago and it’s worth reading/noting.  Adds some “grist for the mill” for the conversation here I think.

WHY THE SET & HIGH EFFICIENCY SPEAKER APPROACH WORKS

DEC 2020
by Steve Deckert

Matching inefficient speakers to capable amps can overcome the loss of low volume dynamics that happens to us with large speakers. 

Something I can speak first hand to. 

My wife is a nurse and works nights, sleeps during the day.  Our bedroom is directly above the listening room.  Fully half the time I listen to my system when she is sleeping.  My Maggies (84 db sensitivity) at low volume give me so much detail and even dynamics that it full out surprises me almost every time!  I've had guests comment on exactly the same surprise that such low level listening can produce such detail.  I also have two REL subs hooked up and the bass at low volumes is ever present.  I fully believe it is a mix of electronics and speakers and I cannot agree with the statement that high efficiency correlates to quality listening at low volumes - Not on my system anyway.