One of my favorite subjects….Thank you for the soap box.
Seriously though…I’m one of those people who keeps my systems running 24/7 – but most of them are servers.
What I recommend for most users is to turn on the PC when you need it – and if it’s going to be used again within 2 or 3 hours, keep it on until the end of the business day.
To save time in the morning, you can set the PC into stand-by (or hibernate) mode (or whatever) and shut off the monitor. That will save the greater portion of electrical power.
Not very scientific, but I hope that helps,
p.s. I have enough fronts on which I have to be scientific. This isn’t one of them.