I have had problems with systems leaving vswp files on datastore if a migration / system was hung and guest / host rebooted.
I found an great way to find all the leftovers, it easy to clean them out afterwards. They can take up lot of space in big prod enviroments.
For this i use the PowerCLI addon to my vmware farms.
Connect-VIServer "localhost" -User "yourusername" -Password "yourpassword"
dir vmstores:\ -Recurse -Include *.vswp.* | Select Name,Folderpath