The only reason for that switch is to isolate the battery from the rest of the trailer's electrical system. I guess you would use it if the trailer is sitting for a period of time and you don't want the battery drawn down by systems in the trailer like the clock on the radio. Frankly I've never used mine.
If you choose to disconnect it while traveling you should verify that the battery connection to the brakes is still active.
2011 Chevy Silverado Crew Cab 4X4
2009 210 WBS