Something specific to bug out with is one thing, but for an EDC, I can't see it.

A briefcase by itself, empty, packs a hefty amount of weight. I wouldn't see that as an optimal approach. A backpack is more ideal as it provides a method for carrying it without taking up one of your hands, which would be crucial.

Briefcases also imply something of value in them by their very nature. Backpacks, not so much.

IMHO