The very problem with the term "social media" is that it doesn't fully disclose just how social these sites are, of which, truth be told, those that believe that they have full control of who sees what of their content on social media, seldom have much real control of it at all; especially if they are a "person of interest" or are part of a protest group that the police or other governmental agencies wish to monitor, or their views are controversial or they associate with people, or seem to associate with people, that do not have a good reputation. Basically, social media, when distilled to its essence, is what appears to be the voluntary posting of all sorts of personal things and viewpoints that are the equivalency of exposing those that post such to a 24/7 surveillance world that will document, analyze, cogitate, and track those members of society that are a priority of those agencies to take an active interest in, so that those that perhaps claim that they value privacy, have actually openly traded their privacy, discretion, and prudence, for Big Brother surveillance, and all this they have done by their own volition, and for free.
Police and justice departments need good and reliable information in order to perform their jobs well, of which, social media sites, have essentially provided them an incredible treasure trove of information about real persons with their real identifies that is not only actionable, but current, relevant, and with seemingly endless ties from one person to another and then to another. Not only that, none of this appears to require a warrant, or a wire tap, or much of anything, other than the assistance of skilled practitioners in the art of collating social media posts so as to pick up trends, patterns, and information, that allow the police to focus more carefully upon the areas that interest those departments. In addition, undercover police agents now know exactly how to work so much better the angles and their sting operations, because so much information has been posted or alluded to, that their ability to infiltrate such becomes a quantum leap easier; not to mention the fact that because of all the social posting and personal information that is so easily and readily retrievable, that the ability to compromise specific individuals in order to take down a group or negate it, has never been better.
While, law and order types are probably delighted that law enforcement is able to mine so successfully those that make public posts in all of the myriad social forums, this should not be looked upon by the general public as wholly an unmitigated good. The reason why, we should shudder at this newfound power is because the law and the justice departments are now through social media very familiar with the intimacies of real individuals; so then, even though there are lots of individuals that are generally considered to be good people, the government as a force of power, could easily create and manufacture evidence that would appear to be quite convincing, against any of them, should they be so inclined, to essentially damage or to manipulate them. That, my friends, is the advantage that the party that has the information, alongside the power already granted to them, can do at any time, on nearly anyone.