A: An insufficient power supply can cause data corruption, and power fluctuations can damage other components.
B: An under-loaded power supply will last much longer and provide more consistent power, which will also extend the life of all other components.
C: When a power supply DOES fail, your computer is effectively bricked until you replace it. A PSU failure also has a significant chance of frying your mainboard too.
I have had both A and C happen. I have since made it a habit to overkill my psu and keep a spare on-site. I have never had cause to regret it, and have had the spare psu save my bacon more than once.
B: An under-loaded power supply will last much longer and provide more consistent power, which will also extend the life of all other components.
C: When a power supply DOES fail, your computer is effectively bricked until you replace it. A PSU failure also has a significant chance of frying your mainboard too.
I have had both A and C happen. I have since made it a habit to overkill my psu and keep a spare on-site. I have never had cause to regret it, and have had the spare psu save my bacon more than once.