Nikon D800E has a 36.0MP Full frame (35.9 x 24 mm ) sized CMOS sensor and features Expeed 3 processor. On the other hand, Nikon D7200 has a 24.0MP APS-C (23.5 x 15.6 mm ) sized CMOS sensor and features Expeed 4 processor.
Nikon D800E's sensor provides 12MP more than Nikon D7200'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 Nikon D7200 and Nikon D800E 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 D800E and D7200 sensor size comparison.
As seen above, Nikon D800E has a 2.4x Larger sensor area than Nikon D7200. Larger sensors give photographer more control on the depth of field and blurry background compared to smaller sensor when shot in same focal length and aperture.
DxOMark Sensor Scores
Both Nikon D800E and Nikon D7200 sensors have been tested by DxoMark. DxoMark scores camera sensors for color depth (DXO Portrait), dynamic range (DXO Landscape) and low-light sensitivity (DXO Sports), and also gives them an overall score. Of the two cameras that we are comparing, D800E has scored 96, 9 points higher than D7200.