For those who want more flexibility in configuring their computer.
If you don't have enough budget now, you can configure some cost-effective configurations first. When the budget is sufficient, you can change your configuration at any time. Or maybe you're a gaming enthusiast and want to keep up with the advanced configuration at all times.
It can satisfy you in the future to replace the configuration that is not yet on the market. Flexible upgrades allow you not to buy a new computer over time, just upgrade the accessories you need.