How Does This Work Again?

For the first time tonight I saw a band of Guardian Angels on the streets of Toronto. From what I could see, they were a group of 5 or 6 guys in their 30s and 40s standing around in the Bloor and Dovercourt area.

How does this prevent/reduce crime? One would assume that most of the criminals would have the good sense to move one or two blocks away from the Guardians. Do the Guardian Angels prevent crime or simply relocate it? Some supporters of the Angels were upset that David Miller didn't exactly put out the welcome mat for them, but if they don't make a difference then why bother?