@N.N., there are at least two failure categories for SMF backup (as currently implemented). One is catastrophic (partial backup due to some resource limitation, with no warning to the user). If the user is relying on that backup to restore their system, they're screwed. Might as well start over from scratch with their forum. The other is annoying and potentially much work to fix (250*N record problem, certain hex strings needing quotes, wrong default for an integer, reserved keywords as field names, and possibly others). These, at least, can be fixed by manually editing the .sql file, but it can be tricky work.
Are 100% of backups bad? No, but a distressingly high percentage are. Should the first thing a user asking how to restore their backup be told is that it's probably bad? Perhaps not, but they should be told there's a non-trivial chance it's no good.