I was reading the sticky post about bypass caps, trying to understand their purpose:
I'm still not totally clear on why it is needed. So there is some impedance in the circuit. Why is that detrimental to the circuit? What is the danger here?The reason for them is "stiffening" of the power supply. The wires on a breadboard, extraneous bus lines on a solderless breadboard, etc all create parasitic resistance and inductance. This resistance and inductance (impedance) of the board resists current flowing from the power supply to the microcontroller or logic IC.
Here is where the bypass capacitor acts like a mini power supply to "hold up" the voltage until the current overcomes the impedance of the power supply lines to feed the IC.