I agree with what is said.
USB drives are okay, and I have used them myself when traveling but that's it and not for daily use between two machines. The other reason besides the possibility of losing the drive and corruption is the USB port is a bit on the slower side, even though they're a bit faster according to the specs due to how the port is managed by the computer. Due to space constrains within my new computer I can't fit all my hard drives inside the case without them cooking due to poor airflow thanks to DELL's new design. With the number of hard drives, I invested in Oyen USB C multi-drive enclosure. This works quite well for regular data, such as Outlook data-files, music files, but it does not work for Trainz. The USB port doesn't like sustained writes for long periods, and I sometimes received timeouts and disconnects which led to a corrupted database. This could also be a stupid Windows power management issue as well, but I couldn't solve it and gave up. I was able to fit one drive okay and you know which one I chose.

Once that drive was placed internally, the speed came back and there are no longer any timeouts. My conclusion is Trainz really pushes that data around unlike anything else we use.
For the small drives, the other issue depends upon the USB drive enclosure. If this drive uses the USB port for power, this will draw more current while the drive is being used. For regular data copying and backups with occasional access this is okay, but with Trainz we're constantly accessing, reading, and writing data which draws more current. I actually saw this occur with one of those cheap USB hard drives. I had a 1TB drive I used for Trainz for a very short time. While using the drive, my USB port and the drive cable got quite hot, and so did the drive.
The other kind of hard drive, such as the Seagate Backup Hub, for instance has its own power supply and a power brick to go with it. This might be inconvenient, but there's no current draw on the USB port. When I do go on the road, well downstairs and on to the back deck these days in the warmer weather, I take my replicated data on my external hard drive and use Trainz and set myself up with a power strip connected to the outdoor outlet and laptop plugged into that. Sometimes, I'm lazy and I will use Microsoft's remote desktop and access my desktop computer from my laptop over the network. This works quite well but the mouse sometimes goes crazy, and I have yet to figure that part out but for overall it works quite nicely from my comfy seat on the deck.