The main purpose of the Upfront presentations is to commodify the network audience in order to make them more appealing to specifically the advertisers that will place their advertisements in conjunction with the network's shows. An important note to make is that, for the network, the "production and sale of audiences to advertisers" is the primary goal of commercial television, not appealing to the actual viewing audience (Owen and Wildman, 2002 in Lotz, 2006). Obviously, this is in direct contradiction with the ideals of noncommercial television.
Lotz describes the importance of the network developing a connection with the audience, to better sell this connected commodity to advertisers. Thus, the impact is apparent - the networks will create the most profitable identity possible, meaning following the path of previous money making shows and ideas. Broadcasters want to present themselves as having a solid and profitable goal for the upcoming television season.
Media texts can shape culture and society by reflecting whatever they present back on the culture that follows and watches them. This creates a bit of an interesting situation, because I don't think many people would argue that network television as absolutely no impact on culture/society. The situation is this - shows that make it onto the television network are more examples of the moneymaking route that the network chose to package the audience to advertisers than are they reflections of what the audience wants and needs as viewers. Because of this, you get shows that try to hit it big with ratings, and consequently the ideals of the shows are indeed reflected in a societies culture.