Christophe,
I finally again located the web article that, in my opinion, best instructs on how to most safely modify your libraries so that the individual files created by applications automatically go to libraries on your documents drive rather than filling up your 2.5 inch form factor or M.2 PCIe form factor boot SSD. The article is HERE.
https://www.pugetsystems.com/labs/support-software/Moving-Windows-7-8-Libraries-184/
Puget Systems is a high end company here in my region, and their support pages have an amazing collection of very valuable articles, which are searchable. The one here is what I used to set up all our SSD based workstations that also needed a documents drive, and I used the preferred method detailed by the author. The documents drive, of course, can be another SSD or a large HDD.
Make sure to keep about 20% of a SSD/M.2 SSD free from files for best performance (or officially use overprovisioning). I believe overprovisioning is supported by the M.2 SSD software that comes with the PCIe based SSD that Brian is using in his Z600. I have one of those coming now for testing on the xw and ZX00 HP workstations....