Have you experienced a Standby Offer from an employer?

I'm not experienced with a standby offer position, but recently I just got a standby offer from an employer and was told that when someone's background fails or unable to attend, i will receive a call or possible for the next training class. I do know that they were hiring for another class after the one I applied for. Just wondering what it's like, how things work, and any positive experiences that you guys might have with a Standby Offer. I want to believe that for sure I get the position, possibly the next class at least.

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