Plotting a course before leaving is fine, but you don't know what you're going to run into out there.
Remember (somewhat fondly) a run from CC Canal to Penobscot - pretty straight forward overnight run. But during the night things changed - wind force, wind direction - in short, we didn't know where we would end up - or when. With the new wind from the N, we were now tacking, looking for a safe harbor. But the idea of going into Porpoise (where we'd never been before) in the dark wasn't appealing. A wind shift to the NE made Portland a candidate, but again arriving there in the dark wasn't a good choice. We kept sailing, and the wind kept changing, and we ended up in Penobscot as planned - after a grand tour of the Gulf of Maine.
Gotta go where the wind takes you.