Summed up in a word: Faster.

I'm a stronger rider than my wife. I got cocky one day and took my hybrid on our long weekend ride so I wouldn't have to "wait" for her. Let's just say it wasn't me doing the waiting. Still haven't heard the end of it from 2 years ago.

In quantifable terms it took me nearly 30 minutes longer to ride 40 miles on my Hybrid versus my Roadie with seemingly less effort put in on the road bike.