Does working in Target Disk mode hurt hardware? I had asked a question on how to connect a MacBook Pro to an iMac such that the iMac gets control of everything and that I used RAM and CPU power of iMac instead of MacBookPro. Here is how I did it: 

Usign iMac as a Display for MacBook Pro


  1) Turn off both devices.
  
  2) Connect them with thunderbolt cable
  
  3) Turn on the MacBook Pro AND keep holding the "T" key on its keyboard. You will see it will go to a disk mode with the Thunderbolt icon showing on its screen.
  
  4) Turn on your iMac AND keep holding the option key on its keyboard. You will see it will show you some hard disks on the display. Pick the one that is for the MacBook Pro.


Done! Now Nothing from iMac is running in the background, iMac's peripherals are working for MacBookPro AND EVEN better: you are using CPU Power and RAM of your iMac to run MacBookPro.

My question is: Does it hurt the hardware of any of the devices? If I connect them this way for like four hours? Or it is just meant to be a temporary connection method and shouldn't work with them like them as a solution?   

My scenario is that when I come home and take work laptop to home and still need to work, I wanted a bigger monitor so I thought, "Oh well let's connect it to my personal iMac."
That won't harm anything.  In Target Disk Mode, your MacBook Pro behaves like any external hard drive.  You're simply booting the iMac from the MacBook Pro's hard drive.  This is exactly the same as booting from a regular USB or FireWire hard drive.

Note: When you do this, none of the hardware on your MacBook Pro other than the hard drive is in play.  The CPU, RAM, etc. are all powered off.  Other than the hard drive, you're still using your iMac.