When the pixels are matched to the optical system, the more pixels, the more sky we can cover. This is independent of the actual size of the chip. Placed on the same telescope, the larger chip would cover more sky. If, however, we select optical systems that image 2 arcseconds of sky on each pixel of both detectors, then the more numerous pixels of the smaller array will provide the greater sky coverage. Furthermore, with both detectors recording the same amount of sky per pixel, the performance of the chips will be very similar.
Different rules apply for planetary work.
Here we typically deal with bright objects and exposures brief enough that little or no cooling of the CCD may be required. This can significantly reduce a camera's complexity and cost. Planet images are also very small, even when recorded with long-focus telescopes. This means the CCD can be small as well. In fact, small arrays have the advantage that their readout time is more rapid than larger CCDs.