Not much. The best way to increase VRD smart edit performance is to save to a different drive than where the source file is stored. The best way to increase recoding performance is to get the fastest CPU you can afford.
If you are encoding that will be the main speed limit.
But as mentioned "from one drive to a second drive.
I found that for simple editing (FAST FRAME COPY)...
Hard drive 4000 fps
SSD 10,000 fps--------Can't remember if that was on a high speed storage device
-----------------------------or a normal Sata SSD.
I now use an SSD for all my qsf, editing, encoding and associated file management operations.
Also gives me faster system startup, lower power bill, less heat, and zero noise.
Can't quantify the difference, but it feels like I'm in the fast lane now, R.I.P the hard drive!
The only real advantage of a mechanical hard drive is space. I think the biggest SSD you can get right now is 1TB, and they are pricey. A 5TB HDD is relatively cheap by comparison. What I would recommend for a desktop user would be an SSD as the main boot/install drive, and then two HDDs (or two RAIDs) for storage. Download your videos to one and output the edited video to the other. That will provide the best performance to cost ratio in my opinion.
Buying an SSD will help speed up many things, but it will not increase VideoRedo performance at all.
My normal rig is a Ryzen 1800x, 16GB memory, a 512GB NVMe 960 EVO SSD and 2TB 7200 internal HDD for storage.
Windows & programs including VideoRedo run off the NVMe drive. I've run tests with the source and output files both on the NVMe drive, both on the HDD and with source on the NVMe and the output going on another 1TB Samsung SATA SSD. Running the same encode gives the same time on any combo of drives.
Encoding is mostly done in the CPU & memory. A small amount of source data is pulled off whatever drive you use, then lots of CPU processing, then the recoded data is sent back to the output drive before another bit of data is processed. At no time is there huge clumps of data being transferred.
My 960 EVO reads 3200 MB/s and writes 1900 MB/s. A typical SATA III HDD can transfer data at 80-120 MB/s.
Monitoring I/O during VRD encoding shows burst activity of 0-25MB/s data transfer. I/O rates during encoding never get close to the HDD max, much less that of a SSD or NVMe drive.
Same goes for VRD and memory. Even running 2 VRD encodes simultaneously, memory useage never reaches 4GB
By all means, get affordable SSD for your boot drive, but spend most of your budget on the best processor you can swing and a large HDD for storage