Since jobs can be some of the most powerful effects in Doomtown, being able to make sure that a particular dude cannot oppose your job can go a long way towards it being a job well done.
of course, the inherent limitation is that it only works on jobs that target locations. This means it cannot help with a Kidnapping, Ol' Fashioned Hanging, Curse of Failure, Mugging, or Forced Quarantine.
So then, which jobs to use this for? Probably the best one to use this on would be Recruitment Drive, but of course they share a value, so that makes it hard to combine.
As for the "not being being affected by the job effects" part, you can use this to keep a disposable dude from being the victim of an Election Day Slaughter.
all in all, a difficult card to make use of, because it requires another card to initiate the job - which eats up a lot of cards. and ultimately your opponent might not have wanted to oppose in the first place.
and that doesn't begin to touch on the stiff competition in the 10 of Clubs department - Unprepared chokes out better cards than this.