In other words, carrier pre-selection gives the telephone subscriber a choice when it comes to the automatic routing of calls across the telephone networks of different telephone companies.

The idea with carrier pre-selection from a consumer's perspective is to save money by having one's calls routed via the cheapest telephone networks. This essential in the building of a consumer friendly telecoms regime, not only because one saves money in the process,  but because one saves money that can be spend elsewhere (school fees, food, etc.).