As SSDs have come down in price, often dramatically, they can be very tempting. You do need to research 1st before you even consider buying, because performance, lifespan, & reliability can vary considerably between brands & models. One of the reasons the cheapest SSDs are cheaper, is that they skip having their own on-board memory, using your PC's or laptop's RAM instead, but that only works if you're running Windows 10.
I was hoping that putting a VM's VHD on an SSD would provide a pretty big boost in performance, because they often seem a bit disk-bound -- seem to have slower performance as they often wait for hard disk reads & writes. Watching Windows 10 Task Mgr. in the host copy of Windows, it's common to see a VM using or causing 100% disk activity using a faster conventional hard drive [a WD Black]. So moving that VHD to an SSD seemed an obvious solution, but it doesn't help nearly as much as I thought it would.
The data transfer rates using an SSD vs. the conventional drive are much the same, though the activity shown in Task Mgr. decreases very dramatically with the SSD. And while the VM does perform better on the SSD, I have to really look hard to notice the difference. Seems most of the bottleneck comes from the overhead of reading & writing to the VHD rather than a real hard drive. Increasing the number of CPU cores &/or RAM allocated to the VM doesn't help.
SO while I was hoping to write something along the lines of spend $20 on a cheap SSD and Double the performance of your VM(s), I was wrong -- my hopes were dashed. It does help, a little, and the difference would be more noticeable if the conventional drive was a slower model, but there it is.