It is obvious to me that decoupling capacitors are necessary in proper circuit design. I also realize that different types of capacitors can be more useful depending on the application. However, I have also read in several places (most recently in Op Amps: Design, Application, and Troubleshooting by David L. Terrell) that decoupling capacitors can completely be negated in their purpose if aluminum elecrolytic capacitors are used due to their higher impedance or the leads are not short enough. This ties directly into my question:
Why do I find aluminum electrolytic capacitors being used in decoupling techniques? Is it bad practice to use them or are these few sources I have read from incorrect in their explanations?