Please see http://forums.musicplayer.com/ubbthreads.php/topics/2045128#Post2045128.

perhaps diff reasons.

First off it gives you an idea of about how much volume to expect though this depnds on speaker efficiency and such..

it will tell you what kinda speaker to shop for if u decided to
replace it with something else... if you only had the speaker handling data u sould not be able to determine what kinda speaker would give u the headroom desired...ex if your amp is 100W and your speaker is 300 w u may have the head room desired while a 100w speaker would distort. armed with no power amp data u would have no idea whether a 100w or 300w speaker is best for u.

if u were looking for more volume out of your package you could mod it by replacing the stock speaker with a more effecient one. if you knew the power amp rating you could calculate in advance what kind of volume u will get with a more efficient speaker. (u would be able to get a db value rather thatn a percentage greater than value)

i suppose the possibilities are infinite..... the most common way of determing wether a powered speaker is right for u is by reading the wattage rating... without that u would have to use some other system to give u an idea of the audio out put... perhaps like a btu but for speakers.....