initValue is the memorized or initial value for that channel, and when you restore (or alt-click the dial), it'll reset to that value.

No, you don't have to use the joint editor or hand-edit the CR2. If you wish, you can set new dial values from Poser's parameter panel and then memorize (via the Edit menu) to retain these changes.

I'm not really sure why it doesn't default to zero. It may have something to do with IK or the Walk Designer.

What's the purpose of initValue? Well, if you like to start your characters from a given pose or with specific morph settings, you can memorize these settings and then do a restore whenever needed to return to your initial state.