Depends on the job. If you suspect it's not a particularly popular destination, longshot could be worth it if you really want that position. If you think other people are applying, don't bother. You know, don't shoot for Duke or UNC as a longshot. It's almost certainly not gonna happen. But if you just happen to like some particular low- to mid-major, you have 4 applications, shoot your first one at your top choice.
If it's keep looking, keep looking.