Internal controls are needed to
1) Protect the cash and other assets of a business,
2) Maintain the integrity of the financial information used to make business decisions and assist in fraud detection; and
3) Maintain compliance with laws and regulations, especially those where being offside can cause major risk to your company.
In small business, the owner can control every single transaction, and this is a very good control mechanism. However, it severely limits the size a company can get.