Hi! I’ve been using this plugin for well over a year, and can answer your question.
It will not publish posts with draft status. Until you shift post from “draft” (or “pending”) to “scheduled” status, they will remain unpublished drafts.
This is so even if a draft is on the calendar. If that date & time comes and the post is still in draft status, it’ll remain unpublished.
I use the calendar just as you describe – as a visual planning tool. I can easily see how many posts I have planned for a given week, and on which days and it’s easy to drag them from one date to the other until I’m satisfied. When I have it all figured out I move them from “draft” to “scheduled” status.
You can move a post from “draft” to “scheduled” status right on the calendar, if you like. Just go to the calendar, and mouse over the post’s title. Choose “quick edit” and you’ll see a drop-down where you can choose “scheduled.” You can also choose the time of day it’ll post.
(Alternatively, you can still schedule a post on the post’s editing screen, just as you would if you didn’t have this plugin.)
And, of course, you can always skip the scheduling altogether and just manually click “publish” whenever you’re ready to do so.
I hope this helps!