It may depend to some extent on where you plan to tour, but I have not generally found that to be a problem. There have been a few times when I have been sick or just exhausted and decided to splurge on a place with more or better amenities, but I don't think advance planning or lack of advance planning was a factor.

The fact that most of my touring has been in rural or small town America may be a factor and I suspect it might be harder to find impromptu camping opportunities in the east. I have not spent much of my touring time near the east coast and when I did we used contacts with family and friends.

If you plan to use Warmshowers or Couchsurfing hosts a bit more planning might be in order, but even then I would be inclined to let them know up front that my schedule is iffy and that I will contact them when I am close by. I find it kind of hard to balance the responsibility to keep potential hosts informed with a flexible schedule. As a result I have decided to use them sparingly in the future. I know that I probably inconvenienced one host by waking him and then bailed on accepting his assistance because we decided we were probably imposing too much on him. (Sorry, Brian in Reno)