I reality, the only real advantage of the alliances is base miles for all. Most carriers interline with each other, many you can get boarding passes for from either UA, DL or AA, none really accept each others tickets without endorsement, few endorse easily with cause (even full fare), none can give you much information about each other, there are no service standards, often times there are reciprocal frequent flyer awards across airlines not in each others alliance, rarely does an alliance partner care much about your alliance status other than checkin or boarding, blah blah blah

I connect and ticket inter alliance and intra alliance all the time and notice no difference. It's nice for me to stay within Skyteam and Star for mileage but that's all I seem to get out of it. I even mix the two alliance carriers one one ticket and use different frequent flyer numbers for the proper respective carriers without problem.