There are two schools of thought, by leaving your computer on the components don't go through a cooling and warming process that can stress the components particularly hard drives where the process of spinning up and down can stress the motors and there was worry about stiction causing the heads to get stuck and solder joints causing them to fail prematurely. This thinking dates back to the days when electronics where powered and driven by vacuum tubes with point to point wiring and hand soldered. So by leaving your computer on, you will increase it's life and reliability. The second school of thought is that turning your computer off when not using it saves electricity and shutting down the computer does not harm any of the components and actually may save wear and tear (on any moving parts such as mechanical hard drives) and that flexing of components is not an issue with modern day electronics.
Me I play it both ways, if I am not going to be using my computer for 2 to 3 days I shut it off, if I am using it everyday I leave it on. It's much easier to do with my Studio since it uses a lot less power than my 2012 MacPro which I did turn off everyday when I was not using it, because it actually had a pretty large impact on my electric bill since it was loaded with 4 4TB hard drives, 4 PCIe cards USB 3.0, eSata, Adapter car for SSD and my Sapphire video card.