Example: You find out you've got a sneaky spammer. You ban him, and then search for certain characteristics of his account throughout the user list (e.g. similar IP / domain, URLs in certain profile fields, etc). I'd LOVE the option to be able to search for them all, select which ones I'd like to eradicate, and then wham, BAN, thank you ma'am! Finding out you've been hit over a month or two by tons of spammers and then having to ban them one at a time is a pain in the ass!