Recently, while working on a client's boat, they commented on the battery On/Off switch. They were particularly curious about the labels on the terminals in the back. One terminal said "Battery" and the other was labelled "Load". "If the switch is just on and off does it really matter which side the battery is attached to?" they asked. Yes, it does matter. In truth, thinking back to electronics theory, there is a good reason for connecting your battery to the proper terminal, and it has to do with how long your switch will last.
In order for switches to last the largest number of cycles, manufacturers design their switches to reduce or eliminate the amount of arcing that occurs between the contact points. When there is current flowing through the switch and you turn it off, it arcs, causing wear to the contact points. In a DC circuit, the current is usually flowing out of the battery to the load; therefore, we know which direction the electrons are flowing in the arc that occurs when the switch is turned on or off. Many manufacturers design their switches with this in mind so that they arc less and last longer. This is especially true for larger loads. Ultimately, you should always connect your DC switches and breakers as recommended by the manufacturer.