Sometimes, why do Chinese characters in couplets lack a little?

This is the running script writing method of "Liu", which is a calligrapher's writing habit and has a long history. The detailed explanation is as follows:

On the premise of not affecting the recognition and reading, calligraphers sometimes add or subtract the strokes of individual words to meet the needs of beautiful layout, especially for simplicity. Such examples are common, such as "Wei, Monument" slightly left on the right; The lower part of "all" is slightly skimmed; Add a horizontal line to the "mouth" in "Jiu, Jing"; In the preface to Lanting, the word "mouth" of "harmony" is also added with a horizontal line and so on.