I use a solid-state drive as my primary drive (C:) and it is 120 GB. It holds Windows 10, and all of my applications (stand-alone programs like Sonar and any of the synths that can run stand-alone, as well as all of the VST plugins). I DO try to keep all content used by the applications off on 1 or more additional hard drives, so as not to fill up the C: drive. This does take some vigilance, but with Sonar, and Office, and Visual Studio, and literally 1206 plugins, plus Native Instruments Komplete 8 Ultimate, and EastWest Composer Cloud - my little 120 GB SSD is only 50% full.
I spent a grand total of $39 for the above SSD, and it rocks - super cheap.
Others that I know have gone WAY overboard with huge SSD drives that are running them like $750-$900, and that makes ZERO sense to me, considering how little is actually NEEDED, with some moving of things around, rather than blindly accepting defaults.
Anyways the above are my thoughts on getting and user a solid-state C: drive. I generally use regular 7,200 RPM HDD's for my 'data' drives - a 2 TB drive of this type is between $60-$75 and holds massive amounts of things like sample libraries and project folders. I have 3 of those - might be a 4th in there. Each of those runs about half full as well, and my system has zero performance issues handling anything I throw at it in a project.
Bob Bone