Fujifilm X100S has a 16.0MP APS-C (23.6 x 15.8 mm ) sized CMOS X-TRANS II sensor and features EXR II processor. On the other hand, Fujifilm X100F has a 24.0MP APS-C (23.6 x 15.6 mm ) sized CMOS X-TRANS III sensor and features X-Processor Pro processor.
Fujifilm X100F's sensor provides 8MP more than Fujifilm X100S's sensor, which gives a significant advantage in real life. You can print your images larger or crop more freely.
On the other hand, please keep in mind that Max sensor resolution is not the only determinant of resolving power. Factors such as the optical elements, low pass filter, pixel size and sensor technology also affects the final resolution of the captured image.
Another similarity between these two cameras is that both Fujifilm X100F and Fujifilm X100S sensors lack anti-alias (Low-Pass) filters. Removing anti-alias filter increases the sharpness and level of detail but at the same time, it increases the chance of moire occurring in certain scenes.
Below you can see the X100S and X100F sensor size comparison.
Fujifilm X100S and Fujifilm X100F have almost the same sensor size so none of them has any significant advantage over other in providing control over depth of field when used with same focal length and aperture.