The most important function of aAlignment is to communicate what belongs together.
Having objects align also makes for a “calmer” design. Imagine that each new place any object has a beginning or an end adds an invisible line to your design. These makes the design more chaotic. Aligning objects is a way to “re-use” the lines so that you don't end up with too many of them.
(Designer here, although I will not claim to be an expert on it.)