MediaWiki redirects are useful if you expect to link to an article or article section using a different title, either with an internal link or an inbound link. An English Wikipedia guideline lists reasons to create redirects. In general, redirects should 1. follow the principle of least astonishment and 2. not be difficult to maintain.
For longer names that include the existing name as a prefix, such as most English plurals, you don't need a redirect. For example,
[[human]]s links to the Human article and shows up as "humans".
Plurals following other patterns should have redirects if the plural is likely to be used often (e.g. Elves to Elf).
Don't over-redirect. We don't yet have a bot to clean up redirects that break after an article is moved. Several articles created as a synthesis of forum discussion are comparisons between two different products, services, or approaches to a solution. We don't need redirects from "X vs. Y", "X versus Y", "Comparison of X and Y", "X or Y", "Y vs. X", etc. Nor do we need all combinations of synonyms (e.g. Netflix vs. DVD, Lovefilm vs. DVD, VOD vs. DVD, Video on demand vs. DVD, Netflix vs. Blu-ray, Netflix vs. BD). For readers already on the site, the search feature will help the reader find the article. But to prevent linkrot and to help readers know where a given page went, we typically don't delete existing redirects except to make way for new pages.