Tandem spinnerbaits offer more flash and lift than do single spins. They are excellent choices when a lot of flash or more lift is desired. More importantly they can be worked at higher speeds through shallow cover when the bass are in an active mood and cruising. When the bass are active and shallow, tandem blades are hard to beat. On the other hand, they are not a good choice for deep water, slow rolling, or vertical drop presentations.
Blades are available in many different sizes.
On most spinnerbaits you can switch blades to achieve different combinations of size, color, flash, vibration, and depth. If the bass are feeding on shad I try to match my blade size to the size of their body. As with all baits, don't be afraid to experiment until the bass tell you what they want. Different conditions call for different sizes, colors, and presentations. Blade finishes can be painted, flat metallic, or hammered.