The most common reasons to choose a tax-deferred annuity are that it allows for accumulation while also ensuring security. Since taxes are delayed till retirement, there is more compounding to augment returns. Upon retirement, the annuity payouts begin. The downside is that these vehicles can underperform during periods when market returns are robust. Additionally, inflation above historical averages would also erode the purchasing power of annuity payouts. 

In contrast to tax-deferred annuities, immediate annuities involve a single lump-sum payment and then payments begin, typically, within a year of purchase. Deferred annuities work differently. After the purchase of the annuity, regular contributions are made. The value of the account grows due to these contributions and earned interest. 

Once the deferred annuity buyer is ready for payments, typically during retirement, the annuity seller begins making payments depending on the terms of the annuity and the total amount of funds accumulated in the account. 

Ordinarily, earned interest is taxed. This is not the case with a tax-deferred annuity. The result is more compounding and principal growth. However, taxes do have to be paid on income received from the annuity or on the accumulated interest, depending on the structure of the specific annuity. 

Finsum: Tax-deferred annuities offer certain advantages such as more accumulation and security. But there are also some disadvantages such as underperformance vs the broader market and inflation eroding the purchasing power of payouts.