Hubs can be used to charge any smaller devices. For instance, you can use a hub to charge phones, tablets, cameras, GPS devices.
There are two ways total amperage is split between multiple ports. In some power banks, there is a total output amperage for the device that is split between the two ports almost evenly. In others, there is a designated maximum amperage per port. This would be clearly stated in the product specifications. Please see the product page for more specific information for each power bank.