Settings - Blox Fruits: game settings

The Settings menu is a game interface, placed next to the Crew option for Pirates and the Ally option for Marines. It groups together the main settings: music, ally visual effects, camera shake, damage counter, codes and Fast Mode.

The available settings

Background Music: turns on or off the background music. Useful if you prefer to listen to your own music or limit distractions.
Ally VFX: when two Pirate players are allied and the option is enabled, you no longer see your ally's attacks, which helps reduce lag.
Camera Shake: when disabled, it removes all screen shaking. Turning it off is one of the best reflexes before doing PvP, to maintain consistent combos.
Damage Counter: displays or hides the damage counter dealt.
Update Log: displayed information about past and current updates. Removed after the 6-week update, it may return next time.
Codes: allows you to enter promotional codes to get rewards (Money, 2x EXP boost, etc.). Codes come out regularly and expire after a while.
Fast Mode: removes all textures to significantly improve performance and reduce lag, especially on mobile.

Good to know

Before a PvP fight, turn off Camera Shake: your combos will be much more consistent.
If the game lags, enable Fast Mode (and Ally VFX if you're playing as an ally) to gain better fluidity.