By itself a parked (and thus not hosted) domain name don't have any value except for being reserved for the future or to prevent other people from registering such domain name.
The most common and easy way to put such domain to "limited use" is to POINT it to somewhere such as to other domain and website that you already have and if you use piet-computers.co.za as your main domain and website due to the separate keyword computers, you can register and point pietcomputers.co.za to piet-computers.co.za. (so both domains will point to the same place, prevent other people from registering pietcomputers.co.za and make up for the possibility that people forget the - separator)
On search engines both parked and pointed domains are however useless because it don't have content of it's own and to add value and use to such domains it's the best to add CONTENT to it and you can do that without costing you a cent or maybe just a small amount.
If your main domain name is piet-computers.co.za but you also have domains like piet-laptops.co.za, piet-hardware.co.za you can create directories like piet-computers.co.za/laptops/ and piet-computers.co.za/hardware/, then add a content page about laptops and about hardware in the directories and point the two domains to the appropriate locations.
With the thousands of free or low cost websites, programs and scripts available as well as the ability of our web hosting plans to allow the hosting of multiple domain names / websites under a single account, you can however create FULL websites for each of your domains and interlink it to each other to maximize the utilization of each and every domain without additional monthly costs.
In above case piet-computers.co.za, piet-laptops.co.za and piet-hardware.co.za can thus be full, standalone websites that still link to each other and also add computer-news.co.za and computer-forum.co.za as goal specific marketing domains and websites.
At a cost of R165 per month (professional package allow up to 5 domains) for all that 5 domains and websites it would have a much stronger and better internet presense than a single website with 4 parked and useless domains.
Of course you can use a single domain for all above and in some circumstances it's better, but the separation under specific and appropriate keyword based domain names allow you much more FOCUS on that specific and appropriate keywords where piet-computers.co.za don't keyword match a laptop section but piet-laptops.co.za is better for all laptop related content because BOTH a keyword in the domain name and content match LAPTOPS.