Minecraft version 1.8.9 is the competitive PvP community's "gold standard." Unlike later versions (1.9+), 1.8.9 lacks attack cooldowns, retains sword blocking, and—crucially for this topic—has a that is client-authoritative in certain respects. This means that while the server validates placements, the client predicts and renders them instantly. Fast block place mods exploit this architectural nuance.
While primarily a FPS boost mod, Patcher includes a "Placebo" block place fix that reduces latency in singleplayer and local servers. fast block place mod 1.8.9