in regards to any electronics or electical device with solder connections they are better to be left powered up the the expansion an contraction of a solder point becomes weak an brittle over time when its tempature goes from warm to cold then eventully breaks like the filament in a light it will burn 10 to a100 percent longer if left on there are bulbs that have been burning well over 50 to 70 years there not special there just never turned off an are on a very stable power grid keeping them at a constant tempature so it is best to leave powered up things are changing an more things are built that have solderless connection just for that reason but not everything an not your pc so for general shelf life of your pc leave it on an run a cool screen saver with a sort of animation to it it will keep pc active an as for stanby thats good if your going on vacaction or long term time with no fuction it keeps board warmed up but uses less power hope this is insightful