Most modern games allow you to bind actions to additional side mouse buttons. This would also be useful in Roblox; for example, my game consists of 2 primary actions bound to Q and E which I could also bind to extra mouse buttons for a better experience. In general, it would make common actions quicker if the player has such a mouse (e.g chat, menu, reload).
I believe something along the lines of MouseButton4 and MouseButton5 would be useful additions to the UserInputType enum.
arent these buttons programmable usually, my side buttons are programmed to normal keyboard shortcuts and keys, this would probably break the functionality