(serious question) why am i afriad to leave my pc running when i'm not home

[grimlock16]

Now,

I do have seti running in the background so its not like its just wasting electricty..

but i want to run some downloads while i'm not home but I'm always seem to be afriad the pc will short out or something and burn down the house .. seems nuts i know but not sure why i can't just leave it running when not home.

 

[TFT]

There's allways that risk if any electrical appliance is left on, most people leave their TV on standby and don't give it another thought but it could happen. Laptops (especially DELL) have been accused of catching fire due to the batteries overheating but many will post on here saying they never or seldom switch off.
Are they lucky or is there no risk, I don't know other than the Power Supply Unit (PSU) would be the only iffy thing that would concern me. Hopefully if a fault occurs the fuse or MCB would trip before it got as far as a fire.
Personally I've never left it on unattended.