The capped corner not only helps a corner look cleaner but also helps combat the issue of turning stitches. Furthermore, it relieves the stress of two separate columns into the same area. The best illustration of this is with the top of a capital letter “A.” The capped corner uses one column stitch from side-to-side across the entire corner area. The columns then come up on each side to meet with the top area. The result is no turning stitches and no overlapping stitches, creating the perfect solution. This capped approach is great with smaller letters. One thing to keep in mind is that the stitches in the capped area are going to be longer than the stitches in the columns below it because the cap goes from side-to-side across the entire letter. This means that when using a capped end, you will reach maximum desired stitch width a lot faster than with other corner methods.
Source: Ed Levy