All of our travel excursions, whether by tour boat, Rick Steves tours, or in our travel trailer, are always made with a complete itinerary. We know exactly where we will stay every night. Our biggest fear is getting into a town and finding every room within walking distance of the train station is booked. Not looking forward to sleeping on a bench at our age. The downside, of course, is inflexibility in the face of bad weather. My question is; can we do our entire trip with few or no reservations? Will we always find accommodations every night in June? Will we have trouble extending a stay, say in Murren or other smallish towns, if the weather will be better tomorrow?
For me, the places I stay are part of the experience (one reason I eschew the "white bread" experience of big chain hotels) so I select the places I stay with care. And I like staying in small towns, which have few places to stay. A lot of people over there know how to find accommodations in advance, and when they do find a place, do they say, "This place is real nice. I won't book it. I'll save it for someone who doesn't book in advance."? No, they book it, and you get what they rejected.
On one trip I tried booking on the fly. I arrived a day early in a Black Forest town where I already had a reservation (this was in March), but didn't go the place where I had reservations, but went to the TI office. They found me a place that was perfectly fine, but it was farther away and cost a little more.
"The downside, of course, is inflexibility in the face of bad weather."
In June? I think in June there would be a far greater chance of everything being booked than that weather might make it difficult to get to where you have booked reservations.
In years of European travel, I've sometimes been flexible and sometimes reserved ahead, but I've never slept on a park bench, and only twice in my car. The only time that I arrived in town and found every bed booked (according to the tourist office) was Easter in York, so I moved on to Yorkshire. Even arriving in Munich at the start of Oktoberfest, a room was available (and pretty clear why; it was a dump). Taking a taxi or city bus from the train station to a further hotel is a reasonable option. Calling or booking online a day or two ahead can also give you options that might be gone if you just show up. On the other hand, if you are used to planning more fully, then summer in Switzerland might not be the time to change your style. I think that a key part of flexible travel is to accept solutions that are not your first choice (of date, price, location, etc).
I've been traveling Europe since the mid-80s and have done quite a bit of it with no reservations ahead of time. The only time I had a problem was when I arrived, unknowingly (completely my fault), in Edinburgh during the summer festival. There were literally no rooms available in town and we ended up sleeping on a couch in the back room of a bar after the owner took pity on us! Other than that we've never had a problem even in major cities in the height of the tourist season.
You just have to be prepared to take what is available, which may or may not be your ideal lodging. In Switzerland it is nice to plan according to the latest weather forecast. The downside is that, in some smaller towns, you may not be able to find a place that can extend your stay.
Maybe do a combination? In the bigger places just wing it and find a place when you arrive but for the smaller places, have a reservation ahead of time and then, if the weather doesn't cooperate, cross your fingers and hope you can extend your stay or find another place in town that has a room. We've often found that, in smaller places, the owners of the various hotels and inns all know each other and can call around for you to see if something is available if they are booked.