[grandsham]

I did that with my first SSD system, mapped C:/Users to an separate HDD. Honestly it was more trouble than it was worth.

Using a junction point for a critical folder like that requires booting into a recovery mode and entering a bunch of incantations into a cmd window. And things will go sideways if you have to remove the Users drive at any point.

An easier course of action is to just use the Libraries functionality under windows and map each of those to write by default into your HDD. so most of my documents reside in D:\media\Documents instead of C:\Users\[blah]\Documents. Then you can also leverage the SSD speed for stuff in your AppData.