There are many benefits of the marketing mix, and reasons why they should be used.
In many cases, it provides a valuable framework for allocating financial and human resources, nearly every company has to allocate a certain amount of its precious resources towards its marketing efforts, and they need to be used in the most effective way.
Also, a well blended marketing plan helps with goal achievement, which will constitute the companys tactical-tool-kit for establishing strong positioning in the target markets.
It can also promote customer satisfaction, by delivering a special customer benefit tied together with each element of the 4 marketing p's/marketing mix. For example the "Price" could be fixed in such a way that imposes minimum cost to the customers, and "Promotion" activities may be designed in a way to properly and completely "communicate the message" of the company to targeted consumers in the correct markets.
There are more and more examples from the benefits of the marketing mix which could be touched on, but those listed above are a few of the main benefits and objectives from constructing a well planned marketing mix, and can provide provide valuable information to marketers and for new projects.