SQLite gives indexes that makes searching and locating previous entries much faster. This is relevant when the history is over 100K entries and one wants to avoid duplicates in history files.
Even if you're on spinning rust, your shell history is probably in cache. You don't really need FST index for this usecase, IMHO.
The DB is at this point 10years old. I use it to evaluate my work habits and patterns. More recently I have started transitioning to a different shell and I used it to move only the functions and aliases I still use, instead of the full collection.