It' fun to speculate about fictional scientific concepts but to be honest, to me they are just the icing of the cake.
One reason why we can have alternate timelines and parallel universes in fiction is because it answers one of the most tempting questions: "What if?" (cf. 2002's The Time Machine
). This is something "real" history cannot answer, fiction can.
That's why I regard conflicting continuities (TrekLit vs. STO, 80s continuity vs. current, 7 ends to the 5YM, etc.) as part of one multiverse - because alternate timelines are sooo much cooler than seeing it from a real-world-perspective. Am I making sense?
Each iteration is more or less enjoyable entertainment in itself but it can have the spacy extra of being interpreted as an answer to "What if?".