Why is steam validating my game files
It simply takes to long and requires too much attention to be practicable.
Reddit user Shawn Maiberger has created a script that verifies all installed Steam games in one go automatically in the background.
This can be after you moved Steam to a new computer or a new hard drive (and the games with it), after you experienced a crash of the system, or after an update of a game on Steam that somehow changed it so that it does not start or work properly anymore.
While you could go ahead and remove games from Steam right away to install them anew, validation is often the better solution.
Once the download is complete you will see an Install button. If the game you are downloading was released after 11/15/2013, your install prompts will look like Option A.
Click on this and it will start installing the game through a Windows installer. If the game you are downloading was released before 11/15/2013, your install prompts will look like Option B. You will be prompted to confirm the uninstall of the game in Uplay. Find the game you wish to uninstall in the list and click on the Uninstall button near the top of the window.
It is using the Auto It scripting language and can either be downloaded as a script or an executable file.
After you are happy with the options on this window, click on Continue. Click on Download to begin downloading the game in the Uplay client. If you close the download progress window, you can always view the progress of the download by clicking on the Download button in the upper right corner of the screen. Depending on the release date of the game you are uninstalling, you may experience a small difference in uninstall window prompts.If the game you are downloading was released after 11/15/2013, your install prompts will look like Option A.