Alignment could refer to alignment of different objects in a design (a website, an application window).
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.)
I am trained as a designer but I actually work as a lookout observer for Alberta Forestry. I spend 6 months a year alone in the woods. Designing and illustrating fills some of that time :)
Here's an article for the interested. Often times, designers will use a grid, like http://960.gs/ offers, to help make layouts with good alignment.
Left, right centre alignment refers to the relationship of text and text frame. You can still have alignment relationships betweens photo and text frame, photo and animation, text frame & text frame, etc.
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.)