SUM Files are Checksum files. When you open the developer menu and start a test of the files, the SUM files are generated complete new. You'll see this in the "More Info" page".
Leaving this page and stop the test, you have a possibility to delete the Checksum files and your Nuvi works as before.
No harm is done.
Moreover, there were reports (but not confirmed) when having old SUM files of a previous map and update this map, the device would become more slowly when navigating. But as written above, its not confirmed