The main feature that requires SIP to be disabled is managing multiple workspaces without animating the swap between them which saves a ton of time and is key to the seamless feel. There are some workarounds of course, but there's no way to get around the 1-2s animation without turning off SIP.
Under accessibility toggling reduce motion serves a similar purpose. It is not instantaneous like yabai but I’ve found it quick enough to not be frustrating as someone who utilizes spaces heavily.
For most basic features, like tiling, Yabai doesn’t need SIP disabled. However, for transparency, borders, and other more complex features, SIP does need to be disabled for Yabai to inject features into the dock.