I am a great fan of not overplanning trips, especially on long road trips, but have come unstuck a couple of times by not doing at least basic research.
It is always worth understanding:
Are there any places that you want to visit which require booking well in advance due to limited availability? I failed to get to the Hal Saflieni Hypogeum in Malta as I booked a cheap trip at short notice and didn’t realize that this, as one of the most popular places to visit in Malta and with limited access, books up several months in advance.
Are any places that you are visiting running a timed entry system. This seems to be more common these days, with some National Parks in the USA doing this. It usually doesn’t cost more than a nominal booking fee, but you have to have a booked slot to gain entry.
Does your destination have any public holidays whilst you are there? This can severely limit your options for access to attractions, bars, restaurants etc. I speak as someone who has been in Belfast on 12th July when all the bars are closed and in the USA on 3rd July when (apparently) lots of businesses close down early for Independence Day on the 4th.
Are any of the places that you are planning to visit very popular and are you likely to turn up at a weekend. If so, it is worth booking accommodation in advance for these places, even if you are winging it elsewhere. Once again, guilty!