If you are not experienced enough to know how far you can push without failing, go for it. That's an important thing to know.
If you have a couple years under the bar and know your body well enough that you know you'll have to bail on it, then rack it.
Looking back at my logbook, I can see the pattern now. Every time I've had to bail on a lift, it set me back a couple weeks. My best progress has always been from those periods of time when I stepped back a bit and started inching back up. The 'easy' weeks have been worth more to me than the really hard ones.
It's been exactly the opposite when I've worked in the hypertrophy range, though. My best gains there have come from blasting it until I couldn't move the weight any more, then cheating out a couple more reps.