Just out of curiosity. What are typical reasons for this? Is it band-related or is it more tactial reasons from organizers? For instance in Weezer's case, they've announced planty of dates already, so I couldn't find any obvious reasons to why they were left out of this announcement.
It depends how much space you need. If it's just one tent, rolling in at 10:30 you'll be absolutely fine - even in prime fields that seem full you'll probably find somewhere for one, if you look enough!