To establish and demonstrate traceability (I will explain the traceability below). Through calibration, the measurement established by the instrument is the same wherever you are, it means that a 1 Kg of weight in one place is also 1 Kg in other places or wherever it reaches. You can use instruments regardless of the units or parameters they measure on different occasions.
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To determine  and ensure the accuracy of instrument readings (through calibration, you can determine how close the actual value is to the true or reference value) – resulting in product quality and safety
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To ensure readings from the instrument are consistent with other measurements. This means that you have the same measurement results regardless of what measuring instrument you use that is compatible in the process.
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To establish the reliability of the instrument making sure that they function in the way they are intended to be – resulting in more confidence in the expected output.
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Provides customer satisfaction by having a product that meets what they have paid for – high quality of a product.