This will increase coverage, help catch bugs, and help to find new performance optimization opportunities.
Currently doing so is neutral except in V8 run using the SunSpider harness, because of a slow-down in raytrace. This appears to just be because of increase compilation time, with raytrace then running for such a short time that it never benefits from the optimized code. We should explore ways of mitigating such slow-downs, but given that this change is neutral for V8 in the V8 harness it's not a huge priority.
Reveiwed offline by Gavin.
Landed in http://trac.webkit.org/changeset/110154