I have bad internet with data caps. So downloading a Steam game at home is not an option for me. I have also noticed the built-in backup and restore options in Steam kind of suck. Normally when I try to use those my home PC still wants to download GBs of data.

But I have learned a trick. I take my laptop to someplace with good internet and download the game I want. Then I move the Steam game onto my home Desktop from my laptop without having to re-download it.
How to transfer a Steam game to another computer
Step 1 – Get the game and update it.
The first step is to download the game onto the remote computer. If you already have it then make sure the game is fully updated. Otherwise, when you transfer it to the second computer it is going to want to download the updates.
Basically, just log into steam and make sure nothing is downloading. Steam auto-updates everything so if nothing is downloading then it should be good.

Ones we know it is updated we make a copy of the game folder to a USB drive or some other storage.

Steam keeps its games in the steamapps\common folder. By default this is located here:
C:\Program Files\Steam\steamapps\common
Step 2 – Copy game files to new PC
Ones you have a copy of the game folder take it to the other computer. Then copy it into the steamapp\common folder.
Make sure you keep the same folder structure that steam used on the other computer.
Step 3 – Install
Now you open up steam and log in. Then click the game in your game list and tell it to install.

After a few

Ones it find all the files the game will pop up in the download list but instead of downloading it will just say it is done.

Now Enjoy the game!
Now you can enjoy the game on your desktop without having to use your bandwidth up to download it!