A 1000ltr of liquid in a plastic tank (ibc), is quite a firm tank. However, as that liquid (or water in our case), starts emptying it leaves space for the water to move freely within the boundries of the tank. Which ultimately gives the wave effect, which is felt when driving/stopping or cornering. This can have a drastic effect when driving.
A baffled tank is a tank with chambers within the tank which breaks up this free movement of water and preventing the wave effect making it a whole lot saver to transport the water.