Importance of Data aggregation in BI

Why do I always have to select aggregation method while adding measure in BI

This is the question many people have while working with BI tools like Qliksense, Tableau, Power BI, etc.. the reason is following.

Say we have a table like following.

Number of immigrant for different countries to Canada

Year  India      China  Australia
2006 30000     5000     300

2007 32000     8000     600

(Above data is not in clean format)

Correct format is 

Year    Country    Immigrants

2006    India        30000

2006    China       5000

2006    Australia   300

2007    India         32000

2007    China        8000

2007    Australia   600