Publishing content to a website owned by a traditional social media company means that you have little rights over how the content is monetized or censored. Moreover, your login credentials are stored on their central database. You have to trust that these companies will be able to keep your private data safe and already we have seen many data breaches from largest Web 2.0 companies (including Facebook and Twitter). There is no way to verify that they are not selling your data.
The technologies powering the Web 3.0 paradigm allow users to retain the ownership of their own data. Rather than publishing content to a platform owned by a social media giant, you are now given the ability to publicize and monetize your content that can be fully independent of trusted third parties. Your login credentials are stored locally on your devices rather than in a centralized database.