The purpose of social media is to disseminate information (sometimes about people) in order to make money. It does not genuinely connect people together.
The disadvantage of social media is the amount of useless information disseminated. When everyone is talking, half the people don’t know what they are talking about. It takes discernment (and a lot of wasted time) to wade through all the useless information and low quality connections in order to find quality information and people who will assist you with your goals and plans.
A far better plan would be to look through scholarly databases for information and attend networking events to meet people. However, said databases may be too limited in scope, outdated, and expensive to access, and the same is true for networking events. Knowledge is moving too quickly for college and business to truly keep up, and that leaves many to choose the more laborious option.
Of all social medias, forums are the highest quality reference source as they focus on a single group of subjects, rather than distracting you with highly irrelevant content like Twitter, Facebook, or YouTube. However, they can still be addictive and distracting - it’s just that the distraction is relevant to your item of research. Unless you are earning money or information off of your social media platforms of choice, it is likely wasting your time and you would be better off using that time to read books or more scholarly references.
Finally, another disadvantage of social media is that the social media companies themselves collect information about you and sell it to advertisers - or whoever else wants to buy. This may not be necessarily wanted by their user bases.