I'm not a great person for keeping unnecessary electrics running during the night or even connected. I'm not paranoia about it, it's just that wherever there is a connection, there is a chance of fire be it ever so remote.
I always not only switch off my computer I switch it off at the plug as well so everything is disabled. If I'm out of the house for a long time say holidays or a long weekend, I disconnect everything which is not essential at the plug.
This is Good safety practice, and I certainly think it's extremely safe and sensible of your friends family.