Schedule says how often and for how long you want JuiceDefender (JD) to turn on data so that your apps that routinely sync data in the background can do so. I've only tried the free version, which limits the user to two options: turn on data for 1 minute every 15 minutes or for 2 minutes every 30 minutes. With Ultimate you can choose other settings, but these two seemed to work okay for me.
The traffic feature basically tells JD to not turn off the data connection if XX amount of traffic has been downloaded in the previous XX seconds. This helps ensure that apps that are in the process of downloading data have the opportunity to complete their download/sync before JD ends the data connection. Downloads won't get cut off midstream. So, if an app is downloading/syncing while you put the phone to sleep by pressing the lock button, JD won't immediatley cut off the data; it will wait until the download is complete. Also, if you have the schedule set up for 1 minute every 15 min or 2 min every 30 min, it does the same thing, so it doesn't cut off a download midstream. In the free version I've left the setting at its default.
Something you may want to be aware of is that some apps rely on being able to download/sync in the background at any time, and JD may interefere with that. For example, Lookout, a program that lets you track down a missing/stolen phone, relies on an immediate data connection. With JD on and my phone in sleep mode, I was unable to locate my phone from Lookout's web page. I haven't investigated the Ultimate JD, but I'd like it to have the option to open the data connection when specific apps that I choose try to connect.