Here's what I think. I think a vision and mission statement help define the "organizational you" - not only does it help people within the organization decide if their plans are hitting the mark ("is this idea really in the realm of what we're all about?"), but also it helps those who are getting to know the organization decide if there's a good fit ("do I really want to be "friends" with you?" "are we of like mind?").
My church is Easter Lutheran Church (www.easter.org). We have well-established mission ("to grow in faith and carry on the work of Jesus Christ") and vision ("transforming hearts and lives for Christ") statements. Bravo - what's even more brilliant is that these statements are so ingrained in our culture that I would bet 80% of all confirmed members (more if you exclude the young confirmed members!) know both by heart. (Yes, I'm on staff, and no, I had nothing to do with it!)
For staff and congregation members alike, we know what we aim to do individually and collectively. We hold all we do up to those two phrases and decide what's appropriate. For prospective members, they get to consider what those phrases mean to them, and decide if we're a good fit for each other. Easter gets to do the same thing with prospective members too, of course. In the extreme, Easter would say, if you're not about GROWING in faith and SERVING the way Christ would serve, then you probably aren't going to be happy here. We do that here. And we expect that hearts and lives will be transformed because of it. Period. As a matter of fact, we say that we guarantee the vision - that transformation - if you are committed to the mission.
Simon Sinek, author of Start With Why, says that in marketing, if you start with the WHY of a product or service (as opposed to the what or how), you gather those around you who BELIEVE the same thing. Now, he's talking from a marketing perspective, but it's the same for vision/mission. Live by your vision and mission and you'll attract those who have the same belief systems you do, and isn't that what it's all about - whether you're an individual, church, or business? For a look at Sinek's material, you can watch the Ted Talk that features him.
If your organization doesn't have a vision/mission statement, why not? If it does, and you're not using it to examine everything you do as well as the people you have relationships with, why not? It could be that your organization (and maybe your life in it) will be transformed if you do!