Answer:
In 1777 (and for a good while afterward), Albany was the most important city in New York. It was (and is) the capital.
It has a strategic location near the junction of the Hudson and Mohawk rivers, so it could control travel down the Hudson to New York City and points south as well as to points west. It also is on the route from Montreal, a British stronghold, to New York city and points south.
Step-by-step explanation:
It would cut off a significant trade and military route from the New England colonies to the Mid-Atlantic colonies. Cutting off this route would have significantly isolated NYC and Philadelphia from possible reinforcements from New England.