SQL Server - backup checksum default vs VSS
This gives you a little bit of extra protection for your database backups, since the backup operation verifies each page for checksum and torn page, and generates a checksum for the entire backup. This is not a substitute for actually restoring you database backups on a regular basis, but it is a useful extra step to help ensure that your backups are actually good.
CHECKSUMs does not add too much CPU load but doing a VERIFYONLY does. There is no impact on vss snapshot creation.