Android is the most frequent mobile platform in the world. This stems mostly from the fact that Google offers its system to everybody who wants to use it. Thus, a large number of manufacturers resort to it. This is beneficial for the distribution of an app, but constitutes a disadvantage because a lot of different devices have te be taken into account.
With an app you are always present on your clients´ devices without the necessity that your clients have to call up another program. Furthermore, your clients are able to retrieve all information immediately without being connected to the internet and you can send them push messages in order to remind them of special offers for example.
In contrast to iOS, Android does not sharply distinguish between smartphone and tablet. Actually, they just have two different resolutions. However, these resolutions have to be taken into account when developing an app, otherwise it may happen that it does not work on all devices.