What do you want to get out of the event? Have you ever been to a convention (comic con, wizard con, etc) before?
With a 1 day ticket you are limiting what you may or may not be able to see. Historically Friday is legends and animation (not 100% sure here), Saturday is Live Action and Parks and Resort, and Sunday is Gaming and wrap up (something else as well). Those are the big stage events. There are two smaller stages that will have a mix of things that are hard to determine what it might be. Last year were things like Goof troop reunion, Inside Out chat, DVC/
DCL/ABD, and many others. Then there are the floor stages that have different things through out the weekend. Again no set there.
If you only do one day you probably won't get into a big big panel if it is Saturday morning. You could probably get into the afternoon panel. I'm not sure if one day ticket holders can over night since I don't know how their tickets are sent. I wouldn't imagine you would want to spend your entire day on a line so shopping may also be limited. Mickey's of Glendale and the
Disney Store often have 3 hour waits just to shop.
With all that said with one day you could walk the exhibit floor, see a lot of cool stuff, and meet a lot of Disney fans. My favorite part of any expo is just walking the portion of the floor full of exhibitors. Nothing like meeting the Dis team (hope they have a booth next year too!) as well as some other Disney inspired companies that I follow online. Nice to put a face to a person. You also get to chat and can get a ton of freebies.