Working together makes use of the skill set and expertise of all the participants (or collaborators) to achieve a common goal. Collaborative or group work or team work is important in a large number of disciplines, whether it is science, engineering, sports, business, etc. For example, a very large group of people (possibly thousands of them) must have worked in concert to develop the operating system we use in our computers (which in itself is a product of team work). In business, someone brings in technical know-how, someone else may be better at managing people, while some other person may be better at managing business, etc. Thus, a combination of people, with different skill set, working together can have a better chance of success than a single person working alone. Technology has made it possible for people to collaborate over internet and work together. For example, if a hydroelectric project in Africa need some assistance, an engineer in Germany can simply assist via skype (or similar program, without the need to physically visit the site). Information can be exchanged in a matter of seconds, over email, etc. Thus, once various requisite expertise are identified, one can assemble a team of people with right skill set and they all can work together to complement each other and achieve success. This is much better than a single person working on something all alone, instead of parallel processing (simultaneous working on smaller fragments, all of which add up to the larger goals) in working together.
Hope this helps.