The terms main and most are similar in meaning, but they don't behave the same from a grammatical perspective.
For example, when used at the beginning of a sentence the expression main uses of the system often takes a definite article:
The main uses of the system include X, Y, and Z.
(This article isn't required, but it is often included.)
On the other hand, the expression most uses of the system would ordinarily omit the definite article:
Most uses of the system are safe and don't involve any personal risk.
That said, when used as an object, the superlative most often uses a definite article:
Of all the uses of the system, X is the most risky and requires stringent safety precautions.