The previous post was quite accurate. I think that the overall effect of corporate censorship is a situation where economics ends up dictating expression. When corporations censor, they end up doing so because of some elements that end up threatening profit making motives or financial results. This would be where profits are threatened by speech or articulated ideas. I think that the interesting element that comes out of this is what happens when organizations that are governed and committed to the ideas of free speech give in to corporate censorship. I can only recommend a film that magnificently deals with this called, "The Insider." In it, a news producer finds a doctor who testifies that the tobacco company is complicit in violating public health and trust with increasing the number and type of additives in the products being produced. Wishing to air the interview, Bergman finds that he cannot as his television network has a business deal with the tobacco company. The film shows in an honest and very powerful way the effects of corporate censorship on news organizations. It also underscores how, in a globalized world, corporate censorship is the only voice that ends up having relevance. Ideology has been put aside for economy.
I think you are going to get a variety of answers and opinions to this question. Most people have highly mixed views on censorship - be it governmental, corporate or other.
Generally speaking, corporate censorship can be looked at as censorship - the prevention of companies or persons within them from basic freedom of speech - at the risk of job loss, fines, other monetary penalties. Those who believe in absolute freedom of speech would argue that this is an infringement of that right. Any of the arguments against any kind of censorship could be applicable here.
I think where corporate censorship is the most prominent is in the television industry. It has been argued that sponsors and advertisors censor things that may result in negative advertising for their product - or advertising for the competition. Many news stations are subject to the censorship of running certain stories or pressured to run them in certain ways. The obvious negative effects here are that what is being shown to the general public on TV is being controlled by capitalism - rather than by humanism or anything else. Some find this a little disheartening.
On the other side however, corporate censorship is a way for companies to protect themselves from comments that come from within that could result in bad press, loss of prestige/reputation, and ultimately money.