>... Why would it be in multitasking?

The function is intended to place windows side by side, if you snap to a side instead of top, you will get half width.
Multitasking in the sense of many windows visible. GUI is graphical USER interface. The whole section is about it. You have a misconception of the term.

>The same lack of general logic applies to things in american supermarkets. Some things are in quite unlikely places. Like lunch bags - they aren't with other paper stuff, not with other bags, but with party supplies (!).

A lunch bag is for work. For a lot of people over there it's as rare as a party. (O.K., I guess those are not so into paper as well)