This is a very good question, because it is so counter-intuitive. I would say that there are several occasions where competition is important.
First, the most obvious answer is that competition make all companies better in the area of innovation. For example, there is great competition in the mobile phone industry now. On account of this, phones are getting better and better by leaps and bounds. The rate at which phones are developing is amazing. There is an amazing amount of creativity and improvements.
Second, competition also makes a company much more streamlined. All the fat is trimmed off. This produces the best work in people. Also within this environment, there can be genuine breakthrough that change the game.
Third, competition also creates for better customer service. Within this context, the customer matters. This is good for the company as well as the consumer.