What do you do with your other electronics.
Hi-Fi, Radio, TV, DVD Player/Recorder etc etc.
Do you leave the TV on 24/7 with the volume turned down presumably.
All your radios and Hi-Fi left on again with the volume down.
Video reorder, DVD Player fully powered up.
All other electronics fully powered up 24/7.
Do you never switch lights off - apart from the bedroom presumably.
What’s so special about the PC?
If you are on broadband with 24 hour connection another good reason to power down unless you particularly want to leave yourself exposed to the hackers out there.
Why pull dust into the PC all the time.
Why push your electricity bills up for no benefit.
In most domestic situations it's a 'no-brainer' to me.
It provides no practical benefit and has nothing but disadvantages.
Electronics don’t like thermal cycling but you can take it too far.
I'd be more concerned about fire risk than some potential increase in the life of the electronic components.
Leaving any significant electrical kit on 24/7 when you can easily avoid it is just a liability, risk and wasteful.