What happens when I put my computer into sleep mode. Is there much energy wastage. Is the consensus to keep it on all the time, although is sleep mode?

   Sleep mode does use a very, very small amount of electricity to monitor when to wake up again.  I had a memory card go bad on my computer after a year and I suspect that it was caused by my computer always being in Sleep mode when I was not using it during the day.  I now put it in Hibernate mode instead.  Hibernate mode does not use any electricity and does not cause wear on any parts while it is hibernating.
   I recommend that you shut your computer completely down at night.  When you run Windows, errors can develop in the background that you may not see.  Shutting down Windows, wipes them out and starts everything afresh the next time.

Thank you. Is hybernate mode the same as shutting it down?

   No, it is not quite the same as shutting down.
   When you click on the Shut Down item in the Start menu, it brings up a window.  That window has a dropdown menu where you can select Log Off, Shut Down, Restart, Standby, or Hibernate.  Standby is sleep mode and Hibernate is hibernate mode.
   Hibernate mode saves the state of Windows in a temporary file and then shuts the computer down.  When you start the computer by pressing the power button, it looks in that file and puts Windows in the exact same state it was in when you hibernated.  All of the programs that you had open will be open at the same place they were before.  Starting from hibernate is faster than a normal start.
   So hibernate ends up being just like Sleep except that the computer is completely shut off (if you were to unplug the computer while it is off, it would not ruin the hibernation whereas it would ruin a sleep) during hibernation, starting from hibernation requires you to press the power button, and startup takes longer than the startup from Sleep.
   In Power Options of the Control panel you can specify what you want to happen after your computer has set idle for a while.  You can choose to have it sleep, hibernate, or a few other options.

You've been amazingly informative as  usual. I learn so much from the responses. thanks.