Hi jellyBones,
If we call Play on an AudioSource or ParticleSystem which are already playing, they restart. In the case of the AudioSource, you would be hearing a “click” instead of the expected sound clip, and in the case of the ParticleSystem, it might be that we would not see any particles or particles each frame.
Feel free to remove the condition with isPlaying to see what happens.
Did this clear it up for you? 
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