With the split cap configuration there's going to be large peak currents (larger than the inductor current's peak) flowing through the caps during the rising and the falling of the bridge voltage ^{(assuming the load is Vpow- referenced)}. The peak values depend on the rate of change (rising and falling). Since the difference of these currents is be equal to the inductor current, there won't be any peaks visible at the load side. However, depending on their values, these peaks may lead to a temperature rise for the caps which may result in extra capacitance decrease. And not to mention possible EMI issues. Slowing down the rate of change by adding some capacitance across the switches might be a solution but it's not always under the designer's control or it's not always possible or easy.

With single cap arrangement none of the issues mentioned above will be present.

The advantage is, as you mentioned, relatively higher effective capacitance. The DC bias of each cap will dynamically change so while one cap has lower capacitance the other will have higher. But the difference may not be that noticeable.

Here's an example:

Assume the supply voltage is 12V and two 1812-case 4.7u/25V (having the following graphs) are used for C1 and C2:

If the duty cycle is 25%: For split cap arrangement, the voltages across the C1 and C2 will be 3V and 9V, respectively. At 3V C1 will be ~4.7u, and at 9V C2 will be 4.4u, so the effective capacitance will be 9.1u. If these caps were in parallel across the output, both of them would see 3V and the effective capacitance would be 4.7u x 2 = 9.4u.

If the duty cycle is 50%: Split cap and the other would bring equal effective capacitance.

If the duty cycle is 75%: Split cap arrangement would bring 9.1u while the other arrangement would bring 8.8u.

So the difference doesn't seem to be noticeable. However, in applications where the capacitor's voltage could be close to their rated voltages then the difference would be more noticeable. See what would the results be for 24V supply voltage.

To me, the benefit doesn't seem to be worth to make the layout a bit more complex.

Assuming you'll have a PI filter in which the L has a non-zero DC resistance, with the split cap configuration there's going to be large peak currents (larger than the inductor current's peak) flowing through the caps during the rising and the falling of the bridge voltage ^{(assuming the load is Vpow- referenced)}. The peak values depend on the rate of change (rising and falling). Since the difference of these currents is be equal to the inductor current, there won't be any peaks visible at the load side. However, depending on their values, these peaks may lead to a temperature rise for the caps which may result in extra capacitance decrease. And not to mention possible EMI issues. Slowing down the rate of change by adding some capacitance across the switches might be a solution but it's not always under the designer's control or it's not always possible or easy.

With single cap arrangement none of the issues mentioned above will be present.

The advantage is, as you mentioned, relatively higher effective capacitance. The DC bias of each cap will dynamically change so while one cap has lower capacitance the other will have higher. But the difference may not be that noticeable.

Here's an example:

Assume the supply voltage is 12V and two 1812-case 4.7u/25V (having the following graphs) are used for C1 and C2:

If the duty cycle is 25%: For split cap arrangement, the voltages across the C1 and C2 will be 3V and 9V, respectively. At 3V C1 will be ~4.7u, and at 9V C2 will be 4.4u, so the effective capacitance will be 9.1u. If these caps were in parallel across the output, both of them would see 3V and the effective capacitance would be 4.7u x 2 = 9.4u.

If the duty cycle is 50%: Split cap and the other would bring equal effective capacitance.

If the duty cycle is 75%: Split cap arrangement would bring 9.1u while the other arrangement would bring 8.8u.

So the difference doesn't seem to be noticeable. However, in applications where the capacitor's voltage could be close to their rated voltages then the difference would be more noticeable. See what would the results be for 24V supply voltage.

To me, the benefit doesn't seem to be worth to make the layout a bit more complex.