HTN Coding 401.0-401.1 or 401.9

Need help:

When you look in the ICD-9-CM book under

401 (Essential Hypertension) it gives you a 4th digit code is required, .0 malignant (Severe high blood pressure; results in necrosis kidney retina; etc or .1 benign (mildly high blood pressure) and .9 (Unspecified ) when would 401.1 Benign hypertension be used over 401.9 Hypertension unspecified?

I know with ICD-10 this will all change

HTN Coding 401.0-401.1 or 401.9