Network effects exist when the value per user rises as the number of users increases. In a situation where strong network effects exist, we often see high switching costs and a lock-in effect. Take eBay, for example. Why has eBay remained so dominant for so long in the online auction market? Well, compare the value per user at eBay to the potential value per user at a startup that might challenge them. Users place a high value on eBay because the existence of many fellow buyers and sellers makes it likely that they can find someone with whom they can engage in a mutually beneficial transaction. They would have a much harder time making that match on a new auction site with a limited number of users. For that reason, the network effects create switching costs for users, and a lock-in effect emerges. That's all good news for an incumbent player with high market share, such as eBay.
Ok, so clearly LinkedIn and Facebook benefit from strong network effects. Does that mean that they will remain as dominant for as long as eBay has in the auction market? I would argue that Facebook and LinkedIn face quite different levels of switching costs and lock-in effects. Consider the cost of switching from Facebook to Instagram or Twitter. What's keeping you on Facebook? Well, it's probably that circle of fairly close friends and relatives with whom you keep up to date and exchange photos and messages via the social network. Suppose that a critical mass of that small circle of friends defects from Facebook to another social network such as Snapchat or Twitter. Would it be costly for you to switch as well? Well, as long as a critical mass of friends has left, then your switching costs are rather low. Yes, you have other acquaintances who might still be on Facebook, but are they really going to keep you there? Perhaps not.
Now compare Facebook to LinkedIn. What's keeping you from potentially switching from LinkedIn to another prospective professional social network? You should recognize rather quickly that your small circle of close friends is not what is keeping you on LinkedIn. Instead, you derive value from a much wider range of users on LinkedIn. Many of those folks are not people with whom you communicate often. They might be former classmates, co-workers, and the like. They are people with whom you share weaker ties, but maintaining a connection to them has potential value to you professionally. Now suppose that a few close friends defect from LinkedIn. Would you consider defecting? Well, the problem, of course, is that all those acquaintances and former associates remain on LinkedIn. In short, the switching costs are higher on LinkedIn. The lock-in effect is stronger. You would be much more reluctant to abandon that expansive "rolodex" that LinkedIn has become for you professionally.
Why the discussion today about LinkedIn vs. Facebook? Consider the latest news from an iStrategyLabs report. It found that the number of Facebook users ages 13-17 have declined by 25% in the past three years. The number of users ages 18-24 has declined by 7.5%. These young user defections show that Facebook's lock-in effect may not be as strong as people once thought. We've seen the story before of a social network losing traction; remember MySpace? I'm not saying that Facebook will face that fate, but it's worth noting that network effects don't guarantee that an incumbent will remain on top forever.