You don't really want to touch these folders because doing so will break things.
What you can touch is the Backups folder.
Each and every time you open up an asset, delete an asset, or update it with an update from the DLS, a backup is made. If you do a lot of updates, downloads and route building, the backups can add up pretty fast and eat up a lot of disk space very quickly.
The default number of backups is 7, meaning 7-days' worth not consecutive days, although if you use Trainz daily then these will be consecutive.
Backups are placed in folders that are arranged by the date in the YY-MM-DD format, and these folders will delete automatically as they expire with the oldest ones being deleted first.
If you are running into a space issue you can delete the oldest folders manually, but the best thing is to set the backups to a level that suits your workstyle. To set the number of backups to keep, Go to the Launcher and then Trainz settings. Click on the Dev tab and enter in the number backups you want.