In the circuit you linked to both C2 (.1 uF) and C5 (10 uF) are used as decoupling capacitors. You may want to
give this a read to understand their purpose. The merit to using a polarized electrolytic is that they lend themselves to getting more capacitance in a smaller package. That was mentioned already in the thread. Also as RCinFLA mentions, for your application you could use a non-polarized capacitor but good luck finding a 10 uF one as it will be big. The reason for C2 is to remove any power supply spikes and prevent false triggering in your circuit. The reason for C5 is primarily to maintain a constant voltage to your circuit.