The Expenditure Method is the most widely used method for measuring the Gross Domestic Product (GDP) of any country. This method compiles the total expenditures by households, businesses, the government, and foreign entities to arrive at the total output produced within a country's boundaries over a specified period of time.

The four main components of expenditure in the Expenditure Method are:

1. Consumer Spending: This encompasses all the expenditures by households on final goods and services and is usually the largest component of GDP. It includes spending on durable and non-durable goods such as clothing, food, furniture, and services including education, healthcare and transportation.

2. Investment: Investment in domestic businesses ranges from constructing buildings, purchasing machinery and equipment, inventories, and equity. Investment is the key component to economic growth as it raises productivity and future output.

3. Government Spending: This component comprises net government investment and the sum of government consumption and total transfer payments. Government spending can either be in the form of money used for direct purchase of goods and services, or for capital investment to build infrastructure like roads, railways, airport, schools and hospitals.

4. Net Exports: This component is calculated as the value of exports by a country minus the value of imports. It is a necessary requirement for any country to have a positive net exports to ensure economic growth.

The Expenditure Method possesses several key advantages in calculating GDP. It is a simple technique that accurately captures the economic activities taking place in the economy by forecasting future economic trends, assess the current economic position, or to review the impact of government policies. Measurement of GDP is also easier under this approach as the government collects data on the four components of expenditure through surveys and enquiries.

On the other hand, this method is also based on several assumptions. It assumes that entities save and/or invest the same proportion of their income, which is not necessarily the case. Furthermore, this approach does not capture some of the informal economic activities taking place in the country, thereby creating an underestimation of the total economic activities.

All in all, the Expenditure Method is the main approach used to measure GDP in a country. It helps policymakers to take effective steps in evaluating the standard of their economy and helps investors to take informed investment decisions.