LinkedIn has a strong B2B (business-to-business) presence. If your customers are other businesses, you more than likely need to be on LinkedIn, because that’s where you will find your audience. The business-oriented nature of LinkedIn also means the tone is typically more professional. LinkedIn marketing can be a good fit for a variety of businesses, but consider your brand and image. For instance, an accounting firm may find LinkedIn is a great fit while an indie recording studio may do better in the more laid back atmosphere of Facebook.
LinkedIn is becoming more popular for socializing, so while there is still a strong business vibe, a shift is happening. You will find a lot of people thinking about business and networking while logged into LinkedIn. However, people likely continue to think about business, at least some of the time, while logged into Facebook.