I have a mid 2010 27-inch iMac which I use every day at home.
When I get up in the morning, I start the iMac to check email, calendar, etc. before leaving for work two hours later, I shut computer down.
When I return home several hours later, I will restart the iMac again, surf the web before dinner, maybe play a game after dinner. Before going to bed, I will shut the iMac down again.
The above process repeats every day. I question is this: which is a better practice? Starting and shutting down the computer during the day, or turning it on once in the morning and shutting it down once in the evening, or not at all?
I've got a better idea. I have a 2009 iMac. It came with a booklet called "Everything Mac". On pages 15 & 16 it has a section called "Putting your IMac to Sleep or Shutting It Down" and gives information as to when to put your iMac to sleep and when to shut it down. If your iMac came with a similar booklet, I'd give those pages a glance and take it from there.