There is always a tendency to choose a higher frequency to reduce the size of the inductor and capacitor to minimize the size of the converter. However, it does not necessarily have to reduce the size of the converter.
As the switching frequency of the MOSFET increases, the switching losses in the MOSFET increase. This requires the use of a larger heat sink, which compensates for the reduction in the size of the inductor and capacitor.
My choice will be to limit the switching frequency of the MOSFET to around 100 kHz for high output converters and to around 200 kHz for low output converters, as this does not require a complex layout and can use components that are easily and inexpensively available. With the development of GaN components with a lower gate charge (and thus lower switching losses), designs with a few MHz are now available on the market.
