I think it depends on your personality. Many people can "wing it" and be just fine. For others, it can be more stressful not knowing where they'll be staying than it will be trying to make that deadline.
For me, I like to have a plan. While I may not make reservations, I would do research in advance and have several places in mind at different intervals so I have a good idea of where to stay. When I'm tired of driving, I don't want to have to drive another hour to get to a place to stop. Having several places along the route in mind, I can easily think "hmm, I'm not real tired now, but there is a nice place to stop in 15 minutes. If I don't stop there, I'll have to drive another 1-1/2 hours for a nice place. I'll stop now."