This is a question I have heard for as long as I can remember.
This argument goes all the way back to my childhood and the early days of computers. Back then, computer parts, especially hard drive, wear out much faster than they do today. So, the argument was that to make your computers last longer, you should always shut it down at nights. My mother would yell at me to turn off the computer and go to bed.
Whether you shut down your computers during the night, is now a personal preferences. If you want your computer to do things like back up, updates or other intensive task, you can schedule them at nights while you are not using your systems. To run these task your computer has to be on.
If you’re concerned about saving energy, turn it off. Or you can use one of your computer has many power-saving modes, which are more convenients for getting it going again in the morning.