2.5 or 3 way; why one over the other?

@erik_squires
Thanks for the info!

Because the two identical drivers sound more "of a piece".

Because it's cheaper to use two identical drivers than buying separate mids and woofers.

These and a hundred other reasons.

Not all 2.5 ways have identical woofer/mids by the way.

Focal Profile 918's used two 6" drivers in a 2.5 way crossover but the top woofer had a smaller voice coil and had better high frequency extension. 

I disagree that 2.5 way speakers are designed because they are cheaper. I think they are good engineering trade-offs for a lot of rooms. 

Answer is simple , if specification say the use woofer , midrange, and
tweeter , this is 3 way,  If specification say they use 3 drivers ,but
mention is 2 woofer with different cross point, or one woofer but
2 tweeters with different cross point , or regular tweeter and sypertweeter . this is 2.5 way. another configuration -woofer , widerange
 with no lowpass crossover , and sypertweeter is also considered 2.5 way,    Some speaker designers looking for something different
configuration ,but is better or not you have to decide using you best
tool is you ear.   But designers is not looking to make cheaper , just different. 

The answer requested is not really discernible from these varied answers. If different - how does ACTUALLY MANIFEST itself. They make different but why - THEY must have reason presumably, but joe public on this list does not know