In some descriptions for Wyeast wheat yeast strains they say "This is a true cropping yeast and a headspace of 33% is needed"... Does that mean you want to avoid the blow off method when using that type of yeast strain? Does this also mean when using those strains you should ferment in a 6 gallon container for a 5 gallon batch?
Actually you left out a key word in their description:
"This is true top cropping yeast and requires fermenter headspace of 33%."
It means that unlike some ale yeasts (or really lager yeasts) that this yeast does all of it's work on the top of the wort. It will/can produce crazy krausen so want a lot of headspace with it or you risk a clogged airlock, blown lid, etc.