I prefer to use oxford comma where I'm writing a long list of items, and those items contain sets within themselves.
For instance, while listing computer brands that include Dell, HP, Acer, Toshiba, Alienware, Compaq and ASUS, I wouldn't use the oxford comma. But if I'm listing out speaker brands like Bose, Klipsch, JBL, Bang and Olufsen, and Altec Lansing, I think oxford comma helps to clarify the meaning intended.
relatedly, there's a little-used rule that lets you use a semi-colon as your list separator if the individual elements contain commas: "My favorite law firms are Dewey, Cheatem & Howe; Robinall, Widowes, & Laffin; and Sue, Grabbitt, & Runne."
For instance, while listing computer brands that include Dell, HP, Acer, Toshiba, Alienware, Compaq and ASUS, I wouldn't use the oxford comma. But if I'm listing out speaker brands like Bose, Klipsch, JBL, Bang and Olufsen, and Altec Lansing, I think oxford comma helps to clarify the meaning intended.