There is also a cost penalty for higher freq in more expensive core materials for the magnetics. Also, EMI typically gets worse. There is generally a cost increase in gate drive circuitry because the reduced time period forces you to switch the gate faster, takes drivers that can push more peak current. As for capacitors: it's not just size, higher switch frequency forces the use of lower ESR caps which are more expensive in order to keep safe power dissipation. Above about 200 - 300 kHz, ceramic caps have to be used.The PWM frequency is a tradeoff between output inductor and capacitor size, and the switching losses in the switch transistor. So just use the recommended or typical values in the data sheet and you should be fine.
Be aware that the higher the switching frequency, the more critical the PCB layout is. Use the recommended layout in the data sheet for the controller if you can.
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