2. Purposes

Mass media can be used for various purposes:

Advocacy, both for business and social concerns. This can include advertising, marketing, propaganda, public relations, and political communication.
Entertainment, traditionally through performances of acting, music, and sports, along with light reading; since the late 20th century also through video and computer games.
Public service announcements.

Negative characteristics of mass media
Another description of Mass Media is central media which implies:

An inability to transmit tacit knowledge (or perhaps it can only transfer bad tacit).
The manipulation of large groups of people through media outlets, for the benefit of a particular political party and/or group of people.
Marshall McLuhan, one of the biggest critics in media's history, brought up the idea that "the medium is the message."
Bias, political or otherwise, towards favoring a certain individual, outcome or resolution of an event.
"The corporate media is not a watchdog protecting us from the powerful, it is a lapdog begging for scraps."[1]
This view of central media can be contrasted with lateral media, such as email networks, where messages are all slightly different and spread by a process of lateral diffusion.
source: Wikipedia, the free encyclopedia