When inexperienced Workfront users see the "Work On It" button, they reasonably assume that clicking it means that they're going to start working on the assignment at that moment. They might also assume that it changes the assignment status to "In Progress". Of course, both of these assumptions are incorrect.
The button really means "I'm on it" or "This one is mine". Under the hood, it sets you as an assignee for the task, and it sets the Commit Date to the Planned Completion Date. That's all.
It seems to me, and to almost everyone with whom I discuss this, that "Work On It" is a really misleading tag for that button. It makes people more reluctant to click it.