Why was the migration of the aryans to india significant?

The Aryan migration to India forever changed the Sub-continent. Even today, half of India speaks Indo-Aryan languages (Hindi, Bengal, etc.), and almost all of Northern India is heavily influenced by the arrival and settlement of the Arians. 
Before their arrival, India was mostly inhabited by the Dravidians (Tamils, Telugus, etc), who have a darker skin complexion. The Dravidians still inhabit the south of India. Aryans introduced more white skin into India, and even today this distinction is visible: Indians in the south have darker skin and Indians in the north have lighter skin.

The Aryans also introduced a numerous cultural features in India, and in fact dominated the Indian culture for a long time (often forming an elite ruling over local non Aryan people).

Accumulating more land so that your country can continue expanding without running into problems such as overpopulation