High rate of investment brings all the above mentioned benefits, which are explained below:

Increased Level of Employment:
When there is a high rate of investment, businesses tend to expand their operations, which creates new job opportunities. This leads to an increase in the level of employment, which in turn increases the disposable income of people. As a result, the overall standard of living of the people improves.

Increase in the Aggregate Demand:
When businesses expand their operations due to high investment, they produce more goods and services. This leads to an increase in the aggregate demand, as people tend to spend more because of the increased disposable income. This, in turn, leads to an increase in the overall economic activity in the country.

Increase in Output:
With high investment, businesses can purchase new machinery, equipment, and other resources to increase their production capacity. This leads to an increase in the overall output of the economy. With increased output, businesses can meet the growing demand for goods and services, which also leads to an increase in the overall economic activity.

Conclusion:
In conclusion, a high rate of investment is essential for the growth and development of any economy. It leads to an increase in the level of employment, an increase in the aggregate demand, and an increase in the overall output of the economy. Therefore, governments should encourage investment by creating a favorable business environment and providing incentives to investors.

High rate of investment brings high level of employment , increase in aggregate demand and increase in output....
Because
If people invest more into the bank...the banks will provide loans to those people who wants to start a new business...
As people wants to start new business they require employees
Hence employment increases....
Again ,employees get wages
As they get wages they demand different types of goods ...
and Demand of goods leads to increase in output...