I don't know. I think it is best to have confirmed reservations. The time for spontaneity is when you are planning the trip.
In 2001, for my third self-planned trip to Europe, the second one since the advent of the Internet, I decided to "wing it" for a few days late in my trip. I had three nights with no reservations. For the first night I had hoped to stay in a small town in Baden-Württemberg, where I thought my g.grandfather had been born. When I got there, I found there was no place to stay (a was very small town) so I went on to the next town on my itinerary and checked into the place for which I had reservations for the following night, and they took take me a day early.
The next unplanned night, I was in a somewhat bigger town, also the birthplace of a g.grandfather. I went to the TI office and they got me a room. I was nice and at a good price. Had I made reservations in advance, and known about this place, I probably would have reserved it.
The last night, I again came into a town where I had reservations for the following night. Instead of going to that place, I went to the TI office and they got me a place. It was farther from the train station than the place I had reserved for the next night, and a little more expensive, but not bad, but I probably would not have picked it if I were reserving in advance.
Two things I concluded from my "wing it" experience.
- A lot of people are making reservations in advance. When they find the "perfect" place, they don't say, "Oh, that's too nice or too inexpensive. I think I will leave it for someone without reservations." No, they take it, and you get what they didn't want.
- TI offices have a rotating list of places, and they give you the next one on the list - not necessarily the best place, or the closest, or the least expensive place, just the next place. If you really want to get the best place, do the research yourself.
Since that experience, I have always had reservation for my entire trip.