CGI companies specialise in producing an alternate version of reality. This can take a huge number of forms, but its probably reasonable to say that, with a few exceptions, the most impressive of these are the ones where the differences are subtle but significant. Take, for example, the Shard of Glass, the iconic London skyscraper currently under construction. Artists drawings can give some kind of impression of how this 330-metre-tall glass-covered building will impact the landscape and how it will tower over its neighbours (the Shard is the 45th tallest building in the world and the second tallest in the UK, after the Emley Moor Transmitting Station in Yorkshire). However, until a few years ago there was just no way to grasp how it would really appear in its context especially not from multiple angles and vantage points.
This is one example of where CGI companies can manage the impossible. By creating a detailed 3-dimensional representation of the section of the city desired, and superimposing data from the Shards plans, it is possible to make a life-like model of the area that can be viewed and assessed from anywhere inside it. This means that the full impact of the building can be understood both in terms of its impressive height, and in terms of any problems that might need addressing before construction actually started. Such use of CGI is vastly preferable and far superior to creating individual artists renderings, which by their nature are costly, time-consuming and restrictive.
With this use of CGI, companies can create mock-ups of their products whether architectural or otherwise and see how they will look and act (within reason) before they are actually made. The software is extremely versatile and powerful, and produces replicas of the desired product that rival photographs in their quality. In fact, it is now becoming increasingly difficult to spot the difference between a photo or artists representation and a CGI model, such is the detail of the processes used.