This is an idea that is put forth by the sociologist Mark Granovetter.  This idea holds that weak ties between individuals are actually very important in spreading information.  This is why, for example, Granovetter argues that it is easier for a person with many weak ties to find a new job than someone with more strong ties.

Weak ties are ties that we have with people who are not particularly good friends of ours.  These are acquaintances who we know relatively well, but not people with whom we are really close.  Our network of weak ties is very important exactly because we are not close to those people.

When we are close to people, we share many friends and acquaintances in common.  Therefore, when it comes to sharing information, we are less likely to get anything new from these people.  We already travel in the same circles that they do and so we already tend to know everything they know.

But with weak ties, we gain access to other social groups and other information that we would not otherwise know about.  If I have weak ties with someone, they will travel in a different circle than I do and will have access to information that I would not have otherwise heard.

For this reason, having many weak ties is important in giving ourselves access to information from many different parts of our society.