Marketing is a numbers game
If your business actively uses social media as part of your marketing strategy you should be as concerned about growing your audience as you are about growing your revenue. Just like Radio and TV you'll want the best bang for your bucks and that means getting your brand in front of as many people as possible. On Radio you'll want adverts around the news or the weather and on TV you'll want your ads to play during prime time or the feature match.
On Twitter and Facebook it's about how many people liked, commented, retweeted, discussed, blogged and shared your content and messages. The more times these events happen the more people your brand reaches.
Each new Follower on Twitter or Liker on Facebook presents a new opportunity to engage, share, educate and enhance that individuals brand experience. Let's not shy away from that.
As marketers our job is to build as big a community as possible around the brand using the tools at our disposal. Everyone wants a bigger slice of the pie and a bigger audience represents a greater opportunity to convince and convert.
I know some people will go on about "quality over quantity" and yeah sure quality control is vital, you need to be talking to the right people. But if you have an engaged audience and an active community you'd have to be pretty confident you're on the right track.