As @IgnacioVazquez-Abrams said, this is a common method for reducing stray inductance which could lead to unwanted oscillations. I have actually seen this method used quite often, especially in circuits more sensitive to excess inductance and oscillations. Simply put, it improves the performance of the filter.
While it is not the case in your particular example, this method can also be used to trim resistance/capacitance values. If the resistance is a bit too high, one might put another resistor on top of it to reduce the equivalent resistance. Similarly, putting a capacitor on top of another capacitor will increase the capacitance.