Firstly high capacity battery will give you much more range than a smaller capacity battery. Most importantly the maximum power band is much longer, helping you climb steep hills on max power for more of your journey.
A larger Wh battery will last significantly longer than a lower Wh battery. This is due to the stress levels put on the battery during use being much lower on the larger capacity battery. A 500Wh battery for example will last up to twice as long as a 250Wh model, and can therefore save you money in the long run.