I did ask a similar question a bit back here but never really had a satisfactory technical answer. Reading through the documentation of xdoc Lars Hellstrom pretty much asked the same question and noted in a footnote (page 47),
Seriously, can someone explain to me why it seems just about every non-math LaTeX environment that doesn’t start a
\liststarts a\trivlist? What good does all these\trivlistsdo?Is it (a) that people just like the basic design, (b) that there’s some deep technical reason, or (c) that people in general doesn’t have a clue but all other environments do that so it’s best to include it just in case?
Can someone explain the technical reasons for adopting such a design and the alternatives?