If you don’t use a snapshot, the files that have changed during the backup will be inconsistent. Whether or not that is a problem depends on your application.
E.g. If you’re backing up databases and your index files don’t match data files or you are referencing between multiple databases, the restore will succeed but your database will be inconsistent and potentially useless.
If you’re just backing up log files, some log files being older than the other is only a problem for legal investigations.