Buying a computer, no matter what kind is an exhaustive process. You need the perfect monitor, the clickiest keyboard, a sensitive but not too sensitive mouse/trackpad. For something that you are paying a premium for, and something that can last you about five years, you want to make the right decision.
However, sometimes you don't have to focus on each part of the assembly. This is when you can make compromises in certain aspects.
There is room for a lot of experiment and mix match of devices when you have a traditional computer over a laptop or an all-in-one desktop. You can choose from a wide variety of cheaper alternatives for monitors, keyboards, and mice without compromising on the CPU. This makes it cost-effective.
There are a few places where such a compromise can work. When you need a large inventory but the use is only of a limited nature, it can work. Apart from that, even if you need just one or two computers for things like occasionally printing something or accounting management, this would be perfect for you.
Call centers:
Call centers need a lot of computers. They largely operate for providing support and answering questions about products. Employees need a CPU, a keyboard, a mouse, and a headset with a microphone. Here you can have each of these accessories wired. So, the keyboard can use a DB9 cable to connect to the computer, the mouse can use a Type A USB cable, and the headset can use the 3.5mm jack.
School computer lab:
Computer education is highly useful. But kids don't need much in terms of the computer itself. So, schools can afford to get basic CPUs, monitors, keyboards, and mice to outfit the lab. If they want to teach students the function of each cable and the difference between them, they can store components separately. This gives them an early understanding of ports and electronic basics.
Small retail store:
If you have a small retail store that sees average foot traffic, and all you need a computer for is simple bill printing and playing music in the store, then you should go with basic hardware, with the peripherals that use a DB9 cable, and USB cables. The speakers can be Bluetooth
Household computer:
If your requirement is not too high end, you can opt for a simple one to use spreadsheets for maintaining expenses and word processors for simple drafts. With an internet connection, you can use it for small tasks like web searches and email. Such computers wireless accessories, but simple computer cable for power and wired accessories.
While you may need more advanced cables and accessories for more intensive needs, you can do with a customized computer for such purposes so that it is inexpensive.
The benefit of using legacy connectors like the DB9 or the 3.5mm is that they give more options for devices. As they are analog connectors rather than digital, it is easier to plug in and use if the port is available.
When you need to connect these cables into newer machines, you can always get an adapter for the DB9 connector apart from legacy computer cable you may need.