All contributions to the qualified plans are made with pre-tax dollars.

The dollars in your qualified plans continue to grow and work for you tax deferred. Taxes are due on all monies during the distribution phase when you start withdrawing money. 

You will be able to add additional money in your qualified plan as catch-up contributions if you are 50 or older.

Many employers match up to a certain percentage of annual salary to incentivize employees to save for retirement as well as to reduce their own tax liabilities. This match can be considered a 100% return on your contribution up to the percent match of employer.

A payroll deduction simplifies contribution to retirement account as out of sight is out of mind.

Qualified plans may allow loans provisions up to a certain dollar amount. Typically only one outstanding loan is allowed by most plans. You may be able to make early withdrawls without penalty if you are a first time home buyer.

The contribution limits are set by IRS which may not be adequate for you to accumulate enough dollars in your plan.

There are penalties for early withdrawls. While money grows tax deferred, you should think about opportunity costs associated with restricted access to your own money.

You will be restricted to the limited investment options provided by your plan provider. 

Whether or not you need money from qualified account in retirement years, you will be forced to take required minumum distributions (RMD) from your account. You may have to pay penalties if RMD limits are violated. IRS is waiting for their payday when you start paying taxes on your retirement nest egg.

While taxe rates have been relatively low in recent years compared to early 1960s, they will be unknown till your actual retirement years which can be a big drag on your retirement income.

By letting you defer taxes in your qualified plan, IRS becomes a partner in your account. While the account grows tax deferred, you are paying for fees and expenses on your share as well as the IRS share of money in retirement account. Taxes are osed regardless of investment loss or profit in your account.

It is possible that you may never use all the money in your qualified plan in retirement. The leftover money in the account does not transfer to your beneficiaries tax free and they may still owe taxes on the money.