You may have some non-income producing real estate investments, such as raw land, which are not giving you any cash flow. You could exchange this for property that is income producing, such as a duplex or a rental home. Not only could you start realizing a cash flow, but you can also get income tax deductions such as depreciation, which you did not have with your raw land.
Often people find that they have been holding properties long after their appreciation has topped out. You can start rebuilding your equity by disposing of those properties and acquiring new ones.
The area your rental properties are located in has become economically depressed or is deteriorating. Why not trade those properties for others in a better location or neighborhood?
If you have rental properties with problem tenants or they are in need of expensive maintenance or repairs, sell the properties and acquire other rentals with fewer problems. This may also give you an increase in appreciation.
Many people think about selling and reinvesting into more income or investment property. One would be foolish not to do a tax-deferred exchange! If you sell and reinvest, you will pay income taxes on the realized gain. However, if you call it an exchange, you will pay no taxes. This means that more money is available as leverage for acquiring your next properties. Look at it as a free loan from the government!
With proper estate planning you can keep exchanging properties throughout your lifetime. Neither you nor your heirs will ever pay income taxes on the gains.
By doing a tax-deferred exchange, you can conserve your equity by not having to pay taxes on your net profits.