failing in a power rack is fun if you're in a gym that doesn't punish you for being loud. the first time i tried 335x1 i had to dump it, and had a similar issue when i tried to front squat 245x1. i'm sure having failed reps all the time isn't a good thing, but sometimes it's fun to see how far you can go with it. i don't see any danger in failing on a front squat.
personally, i've been doing 5/3/1 for my back squat, so there are those built in "or more" sets where you can push it to the limit if you'd really like to. sometimes i go for only smooth/explosive reps, but sometimes i'll keep cranking them out till i feel like i'm gonna pass out.
some guys who are more jacked than me might have something different to say, but those are my experiences