Is there any difference in that what grid size is chosen?
Yes, there is difference.
At first, if you cut the structure by grid for proximity correction, the calculation time depends on grid size. The smaller grid size the faster proximity correction calculation. But the smaller grid size the large number of grid cells and the large file size. For the big structures this can cause problems. So, better to choose compromise grid size in range of 20 - 100 um.
The other destination of grid is the cutting of structure into subfields for exposure with stage displacements. In that case the recommended grid size is close to uniform? writefield size, i.e. about 50 um or a bit large. The smaller subfield the much accurate beam shape and trajectories but the large number of subfields and stage movements that will lead to increasing of total writing time.