sentential relative clauses- referring to the whole of the previous sentence

Some relative clauses refer to a whole clause, a whole sentence, or a longer stretch of language. We always use which to introduce these clauses.

They stayed for the weekend, (and) it was great. – It is grammatically correct, accurate…but something like this would sound better, especially in writing: 

They stayed for the weekend, which was great.

Something similar would happen with these sentences:

Some users do not think twice about the comments they post on social media, and this may have dreadful consequences.

Some users do not think twice about the comments they post on social media, which may have dreadful consequences.

Interactions between people who are near to each other are reduced and it could be dangerous for true relationships.

Interactions between people who are near to each other are reduced, which could be dangerous for true relationships.

Watch this video for further explanation: