There are two modes of operation, one can be classified as a services company and the other as an ISP.
As a services company your primary use of IPplan will be to manage individual IP address records and the address plan of one or more customers.
In ISP mode, you will assign blocks of IP address space to your customers. In this mode, you will not be concerned at all with individual IP address records and how the customer breaks down his assigned address space. When you operate as an ISP, you may also generate SWIP/registrar entries, which are only useful if you deal directly with ARIN or any other registrar. (SWIP is enabled in the config.php file, see ARIN tutorial for more details). All the relevant SWIP/registrar information is entered when the customer is created.
When using this mode, I suggest creating a dummy customer which holds all the allocated address space from your regional registrar (ARIN?) already broken up into the various blocks that you will eventually assign to your customers. All these blocks should be called "free" to allow them to be found using the "Find free" menu option. Once you are ready to assign a block, create a new customer with all the relevant SWIP/registrar information completed, go to your dummy customer and move a block of address space to the newly created customer, and finally generate a SWIP/registrar entry for the new block. In this mode areas and ranges are not too relevant except for the dummy customer (see concepts below). You may also need to create a template for your registrar in the templates directory. If you have done this, feel free to contribute it to IPplan.