Assuming I use it all day long, should I shutdown my (recent) laptop every night and power it up every morning, or just let it sleep by closing it?
To determine the power used when the computer is in sleep mode you can acquire a power meter that plugs into a power outlet & measures the electricity used by devices that are connected to the power meter.
This has been done by one person who posted the results online. The summary states:
The standby mode power consumption is just a bit more than leaving the computer plugged in but off. So I can use standby mode without any significant additional cost.
While I'm away for more than 8 hours it makes sense to turn the computer off at the power strip. At this point no electricity is being used by any of the devices on the power strip. I usually do this when I am done using the computer in the evening or plan to be away for a while.
The reason why the computer uses power while it is in sleep mode is because all the computer processes are stored in RAM, which requires powers to maintain things in memory.
It comes down to you. Do you want to use electricity keeping the computer's memory active while you are not using the computer for long periods of time and then to have the computer be instantly available when you open it up again, or do you want to use no electricity and wait for the computer to boot up and go through its initialization procedures when you turn it on, after not using it for a long time.