You can set the category view on a per category basis, an example of where you may want to use this could be with your main categories where you would want to display the products in gallery view, and then your accessories category could be set to appear in list view.
This is usually the default view setting for your categories. As you can see below, the advantages of using Gallery View include that the product images are large and show off the features of the product, the price, short description and More Information as well as an 'Add To Basket' button can be included in this view.
The List View option will use less space on the category page, allowing for more products to be displayed at once. As you can see in the screenshot below, the product images are far smaller than they appear in the Gallery View, though you can still display a short description, the product price and both the More Information and Add To Basket buttons.