80% is high enough to be safe, that if you leave it and forgot you have lossy change enabled, it won't ruin your images.

I want to add better UI for enabling lossy optimizations - #17 and then I'll be able to allow more risky settings.

Lower quality added in this build: http://imageoptim.com/ImageOptim1.5.3a1.tar.bz2

Thanks for this build, really useful, but you've still limited it to 70% max compression for jpegs. Any chance you can create a version that can compress down to 20-30% compression for JPEGS? Thanks! 👍

Like I've said in earlier comment, 30% can be potentially destructive and it's problematic for an app that's designed for lossless optimizations.

If you'd like to see that feature, help design UI that won't make somebody accidentally ruin their images, even if they're in a hurry and didn't read the manual — see #17