The key thing to keep in mind is that everyone has the right to enjoy the parade. Claiming common territory and obstructing free movement is the main problem. Such obstructions can be created by ladders, ropes, or clusters of lawn chairs like the one we had to deal with last night. I'll try to provide a photo later. Somehow it didn't make my latest Flickr upload. (Never drink and organize photos)
Update: Here it is

Just ridiculous. Most of the people utilizing these chairs were in their teens and pre-teens. No healthy child needs to sit through a parade like that. The chairs block street access to other parade-goers AND obstruct the intersection for emergency vehicles. It needs to stop.