Why do you need so much power?

I have a basic question.  I have a set of Tannoys with 93dB sensitivity. I’m told that a 25 Wpc amp like the First Watt J2 can power it just fine. (I don’t crank it to 11.). Someone also suggested an Emotiva amp with 500W RMS. 

So my question. Assuming you have a good set of speakers that are efficient (>90) and you don’t crank it till it’s clipping, then do you ever need such power as the Emotiva?  Thanks!