Optimize, optimize, optimize!
And this little tool helps you with just that!
Epic once made a tool for Photoshop called the “Crop E Assist” which can be found here: UDK | CroppedEmissiveAssistant
But nobody ever mentioned it being usable for UE4.
Since later Photoshop versions have an issue with the file name and a few things in the script, I updated it and made it available here: Dropbox - CropEAssist.7z - Simplify your life
But I didn’t stop there!
The “Texture Cropping” node is still available in UE4, but works a tad… outdated and weird, so I simplified it, and created my own version of this Material Function!
The function can be downloaded here: UE4 - Luos's Cropping Tool
Just pay zero dollar if you don’t want to donate 
It comes with some example content to see how its set up.
Buuuut… I didnt stop there either!
I made a tutorial on how to use it, together with the “Crop E Assist tool” which can be viewed here:
This can drastically reduce texture memory. (up to a few 100mb per project!)
Enjoy
*How to install the Crop E Assist:
Download and install Adobe AIR , or Adobe Configurator . Adobe AIR is the plugin required. Configurator is a tool for Photoshop that allows you to create custom panels.
Navigate to: [Photoshop Installation Path]\Plug-Ins\Panels and copy the Crop_E Assist folder into the \Plug-ins\Panels\ folder within the version of Photoshop you use.
If Photoshop is running, restart it. Once its restarted go to Window > Extensions > Crop_E Assist to open the panel.
*