The question was asked over on the Widow site and someone wrote that the longbows should be unstrung because of their thicker core.
Ken Beck responded with:
"Denny is correct. See page 12 in the Owners Manual. Leaving a longbow strung will not cause serious damage (our showroom bows are left strung all the time),but this will cause them to loose a pound or two over a period of time. Besides,unlike a recuve, there is virtualy no risk of damaging a longbow in the stringing or unstringing process. Therefore, we do recommend unstinging your longbow between shooting sessions."