As far as security goes a computer which is on at any given time but not connected to the internet at that time is as secure as one which is turned off, computers which are permanently connected are perhaps a little less secure that those which are disconnected from the internet or turned off when not in use simple because the latter have a smaller time window in which bad things can happen. I personally take the view of turning off computers each night and turning them on again when I next need to use them. As far as lifetimes of hardware go I do not think there is significant difference between those of machines kept on permanently and those turned on and off daily, each course of action has some advantages and disadvantages to it which approximately cancel out to leave either course about as good I believe. As far as updates go, you don't have to leave a computer on overnight to deal with these, you can manually* check and install updates to the OS and to programs at any time you like, perhaps straight after turning on in the morning or just before turning off at night. For windows updates it is usually fine to just check on a tuesday evening/wednesday night, as that's when they are released.
*thesedays having updates for windows set to "check automatically but ask [you] whether [you] want to download" is very wise, given that:
A ) many of the present windows updates being released are unwelcome and many users will want to avoid certain ones
B ) updating manually lets you get updates within hours whereas automatic update is usually a few days behind (you just have to given yourself a reminder alarm).
Also in light of recent events with KB3139929 ms has been putting users in a "damned if you do, damned if you don't" position. For other programs, browser/antivirus/... ,fully automatic updating is usually best.
Edited by rp88, 10 March 2016 - 08:44 PM.
Back on this site, for a while anyway, been so busy the last year.
My systems:2 laptops, intel i3 processors, windows 8.1 installed on the hard-drive and linux mint 17.3 MATE installed to USB