There are three main reasons for the crowding out effect to take place: economics, social welfare, and infrastructure. (Investopedia)

When government expenditure displaces or crowds out an equal amount of private expenditure, the crowding out effect is said to be complete or total. (Micro Economics Notes)

Because crowding out leads to decreases in private sector consumption and, therefore, slows economic growth, the crowding out effect should be a serious consideration for any government that plans to get an increasing percentage of its funding through the capital markets. (Investing Answers)