The phrase "a primary use" is correct and usable in written English.
It can be used when discussing the main or most important function of something.
Example: "The primary use of this software is to enhance productivity in the workplace."
Alternatives: "a main function" or "a key purpose".
The OneNote app is particularly interesting, suggesting that Microsoft sees note-taking as a primary use for a tablet.
There must be some line where such "devices" no longer have a primary use as a copyright infringement device.
A primary use of the estimated regression equation is to predict the value of the dependent variable when values for the independent variables are given.
Crime fighting is not emphasized as a primary use as the cellphone industry introduces more and more camera phones capable of taking a quick snapshot and sending it wirelessly to the Internet.
First Solar, the second largest maker of solar panels worldwide, explicitly disclosed that a primary use of its 2006 IPO proceeds would be to engage in acquisitions to achieve vertical integration.
They tend to favor a quadcopter structure, and are often configured with photography in mind as a primary use.
What I've learnt in the process of trying to engineer serendipity is that it is tough to put forward serendipity as a primary use-case.
The founders see a few primary use cases for its service.
A second primary use of the concept of historiography is more present-oriented and methodological.
A better primary use of the woodlot would seem to be production of building poles and construction beams which are hard to find in the natural woodstock.
The 61-year-old Drake Tower in Center City is undergoing an interior renovation in a conversion from its primary use as a dormitory to an apartment house.
