For example, I only buy/use old high-end (for their day) business class laptops and put linux on them. They work for everything I need to write and surf.
I also bought an iPhone that was already a few years old and plan to keep it until it stops getting security updates from Apple. I also moved from Android to Apple not because I like iPhones better (I don’t, really), but because the years of security updates (versus maybe one or two, on Android) matters to me.
Not mentioning that you can easily be sure that you can save money by choosing your components right.
Buying prebuilt often skimps on graphic card. But putting in in more memory and cpu to make seems like a better choice.
An other example is pay for midrange(or higher) for a power supply mean you may not need to upgrade for really long time.