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Some parts are more affected by excessive use over time than others. In computers and games consoles, GPUs and CPUs will often fail after excessive use over time if they are not properly ventilated and thereby cooled. When buying such used parts, you often don’t know how much they have been used already. Moving/mechanical parts (e.g. hard drives, drive belts, switches) will often be the first to fail so when you buy them used, you don’t know how much lifetime they still have in them.