For Lr it can be a real help if you can have the Catalogue and previews on a fast SSD, especially if you also have a high DPI monitor. Lr now defaults "standard" previews to match the width of the monitor. For me with my 5K display that means my previews are 5120 px wide! that is actually greater than 100% for all my cameras, let alone any of my old 300D images that might have been cropped a bit. This can make for larger images to move about, and also means that you can end up using a lot of space too. Although the new compressed lrcat file is down to 5.8 GB from over 20 GB, but with just over 50,000 images my image previews stand at 69.1GB.
Since it is really not good to be almost filling your system drive too full, I have been forced to move my catalogue to my spinning disk for now. The system disk with a formatted 221 GB was down well under 30GB, and it was affecting overall performance. The worst bit was when the last Lr update, which required a catalogue update crashed during that process, because it tried to duplicate my preview files. At one point I thought I had lost the lot, but fortunately it was only a wayward lock file that was stopping both the old and new versions opening the old catalogue, or even the recovered backup.
An additional M2 SSD, along with a PCIE adapter card is now on my christmas list.
Having the CR2s on an internal spinning disk is not really an issue though.