It depends , some people do to show off to prove their superiority on others, some people do just because they are want to share their ideas and life experiences so that other people will learn , some people share on social sites because they want their voice to be heard in the society which is ignoring their point of view on any thing like social values and politics etc, some people share just to use and remain connected with loved ones or friend or social circle.. so it depends on the person who is sharing their life on social media ..but whoever may be the person it bring comfort to their mind because they will get frustred if they will not , they will feel themselves alone and human is social animal who can't live in loneliness.
