Briefcase takes a list of candidates however you happen to have it, writes the assignment email with you, and sends each person their own copy with the brief attached — then keeps a searchable record of every send. It exists for the moment a week later when someone asks "did we actually send it to Priya?"
You're hiring for a Flutter role. You have a PDF brief, forty shortlisted candidates, and a deadline. Doing this by hand means forty copy-pasted emails, forty chances to attach the wrong file or address someone by the wrong name, and no reliable answer a week later when someone asks whether it actually went out. Mailing everyone at once with a bulk BCC solves the tedium and creates a worse problem: every candidate can see who else you're considering.