Some circuit like Voltage Regulator circuit are not force you to use its exact recomended value capacitor. You can roughly decided on it. Circuit like filter circuit do force you to precisely use the recomended value as sketch in the circuit.
For example, you are planning to build 12Vdc to 5Vdc converter. The you start searching for the circuit in the web and you find some circuit. They are basically using LM7805 but with different value of capacitor. Figure below show some of the circuit on the web: