Minecraft's server tick rate is 20 Hz (20 ticks per second). All hit registration, damage calculation, and combat resolution happens on tick boundaries. If you click 40 times per second, the server sees 20 clicks per second — the other 20 are dropped. Combat exchanges are also capped by hit cooldown (introduced in 1.9) which limits damage-per-hit if you click too fast. On 1.8 PvP servers (Hypixel, Bedwars) the old system rewards raw CPS. On 1.9+ modern PvP, the sweet spot drops to 6–10 CPS to allow full charge attacks. Read the Hypixel click policy for the current allowed techniques.