I'd guess that I do more "research" than "planning." I usually have a list of roads I want to ride and places I want to see. I usually have a daily mileage target in mind. Once I'm on the road, I usually know where I'll end up at the end of the day, and tomorrow I'll figure out tomorrow.
Do I know exactly where I'll be at the end of each day? No.
Do I know approximately where I want to be at the end of each day? Yes.
But if I only have a week of vacation (weekend + 5 week days + weekend = 9 days) and I want to see a dozen places scattered 4,000 miles apart, some "planning" is involved, at least for me.
I tend to research and prioritize what I want to do. If I only have 9 days of vacation, I can't spend five days hiking around Yellowstone; I just don't have the time. If I want to see several places — say, Glacier NP and Yellowstone and the Badlands and Rocky Mountain NP — then I have to have some sense of time management: what can I see in 9 days? Logistics are just part of the trip. Logistical problems fall under the "planning" aspect of my trips.
If you have no destination, then maybe you can avoid planning altogether. But I tend to have specific places I want to see, so I need to plan some of the trip.
Just my $0.02. Everyone is different. And I think everyone figures out what's best for them after their first trip. There's no right or wrong way to take a trip. All that matters is the ride. Enjoy every mile!