Shrub zones are designed specifically to water your planting beds and not your lawn. Plants have different watering requirements then lawn so a shrub zone will allow you the ability to control how much water is on your plants. The zone itself is not plant specific. All plants within the zone will receive the same amount of water.
A standard shrub zone covers most standard sized landscape beds. The zone can be as small as one sprinkler head and as large as 10 sprinkler heads. The rule of thumb is that one shrub zone will usually take care of the front landscape bed and the back landscape bed would need a zone of its own.
If you plan on having a landscape bed in the front of the house, typically in front of the window, as well as within the sidewalk area up to the house, one shrub zone would cover that area in most circumstances. If the beds are relatively large, you may need two zones to water that area.