I'm always going to stand up for Express - y'all know that.
1. Everyone always loves to dog Express, but I don't think Mainline wouldn't exist without it. Where are we going to get all of the customers to fill all of those big jets without Express hauling them in from the AVLs, EWNs and YUMs of the world?
1a. I want to dispell a myth here: People frequently say Express agents (I'm talking Piedmont where they do ground handling) are inexperienced, clueless, rude, etc. Before I left US/EN, I used to manage complaints for the Express network. The fact is, in CLT and PHL, the complaint rate for Express was better than it was for Mainline! And this wasn't a one-time deal, either. This was sustained over the course of more than a year. Now Mesa in PHX was a whole different story. Not so much with them.
2. Express has a lower payscale, lower operating expenses, etc. and therefore has a lower CASM than Mainline. That makes it possible to operate into piddly places like AVL, EWN and YUM that wouldn't otherwise be able to economically support a full-sized jet.
3. I do not like the fact that US has Express flying some ridiculously long routes. I recall having to get creative to get home from PHX once and I ended up on CR9s all the way. I think it was PHX-MCI-CLT.