Many chips, like a bluetooth chip, don't draw power continuously, but there are spikes. These spike in current can lead to the voltage dropping to low. A filter cap acts against that.
Sometimes, especially in prototyping circuits, where nobody took care of properly designing a power supply, filter caps are the first cheap shot at fixing weird behavior.
If you wanna know more, google the term, there is way better explanations then mine, form people with way more profound knowledge.