In many countries, such as the U.S. and the UK, the tax law provides that the interest on this cash value is not taxable under certain circumstances. This leads to widespread use of life insurance as a tax-efficient method of saving as well as protection in the event of early death.

In U.S., the tax on interest income on life insurance policies and annuities is generally deferred. However, in some cases the benefit derived from tax deferral may be offset by a low return. This depends upon the insuring company, the type of policy and other variables (mortality, market return, etc.). Moreover, other income tax saving vehicles (e.g., IRAs, 401(k) plans, Roth IRAs) may be better alternatives for value accumulation. A combination of low-cost term life insurance and a higher-return tax-efficient retirement account may achieve better investment return.

Reference: www.wikipedia.org