It depends on how the PR, project or comment thread interprets the -1s. If a vote has been specifically requested then the +1/-1s are super useful. Otherwise they could be safely ignored by maintainers as at most low value ambient info ... well worded constructive criticism will always carry more weight that a -1. Also, this is fundamentally different to SO/HN ... there is no ranking, the up-vote/down-vote ratio has zero effect aside from incrementing a counter - any meaning applied is subjective.