I use externals for everything.
Over the past few years, I slowly got out of storing anything other then programs themselves, or the current project I am working on, on the internal drive.
Once I complete a project, it gets moved onto one of my externals.
I use 2x 1TB WD MyBooks, and a 2TB one. All partitioned a few times.
With that now I still have 2 internal drives, I have a 128GB SSD that is for my OS and major programs only, and a 1 TB partitioned for other programs, and the blank partition is where I store the files of my current project.
My seek and load times are practically non existent, and even loading or saving large files is reduced to minimal times.