Span and p(aragraph) styles format text. However, on this wiki, all formatting is standardized or otherwise accomplished with a simpler method. P styles are needless since we don't make paragraphs, and span styles are really only useful for tables.

In general, when span styles are used , they spam the page up, without contributing anything. Usually they're a long tag string saying "format this text normally". This is often left from your editor, especially if you copy-pasted something from MS Word. To improve the quality of our formatting, I have the following suggestions:

  1. Switch to source mode editing (to the top right of your in-browser wiki editor, also permanently changeable via Special:Preferences > Editing). This improves your editing overall, and for styles, it allows you to see how much clutter is created.
  2. Use a plain text editor like Notepad instead of MS Word, to prevent the creation of span styles in the first place.

tl;dr Span styles are bad, don't use them. Switch to source mode editing and get rid of them.

Additionally, here is a general resource for this wiki's formatting, by an active bureaucrat on the wiki.