In the end, these accent lights will get all the glory in the kitchen because they illuminate the focus of the room. The basic rule of lighting pendants is the rule of three. This is basically the idea of balance which is to repeat an element three times. The human brain thinks in patterns and it seems that three is the most basic of the pattern of balance.
However, the rule of three comes second when considering scale. A smaller kitchen with a smaller island may need two large pendants rather than three. If you used three large pendants the room may seem overwhelming and detract from the actual focal points.
Finally, you'll have to consider the amount of light the area requires. Getting lighting pendants with too little light will make the room appear dull and dark. Pendant lighting can also add a splash of color to the kitchen. With wood and stainless steel appliances a pendant can be made of colored glass or some other colored material. This just accents the room, but shouldn't overtake the entire theme of the kitchen.
Pendants can also be used purely for an architectural or aesthetics sense. These unique designs are usually custom made with a theme in mind. They also offer more eye-pleasing views rather than needed illumination throughout the room.
Regardless of the lighting pendants duty, they can play a key role in tying the entire room together. It's important to use the lighting fixtures correctly, though, as they should always highlight rather than becoming the main focal point of the room.