The answer depends on the circumstance. i spent a year or two as a consultant and worked on several shotgun grant campaigns. All of them failed and were a waste of time and money. I discovered that I could usually achieve better success when I devoted time to cultivating a relationship with a funder - calling them, discussing their interests and resources, talking about possible projects. I often learned that a foundation wasn't terribly interested in my particular project or if they were over-extended; thereby avoiding the waste of grant production and submission.
I currently work for a nonprofit and, every once in awhile, I'll send a blind letter to a foundation if I happen to have a prepared grant that matches their interests. I think it's good to get your product in front of other eyes so you can hear different comments but it can be a waste of time and resources if you don't control it.