As for negative use, I'm not entirely sure what you mean by that. I can't remember any specific incident when I've made a personal negative decision based off of applying logic (there are plenty of misapplications, but that just comes from misinformation). Sometimes I will misjudge something and screw up (misjudging the consequences of something), there are a few other things that I can't think of right now (it's a bit early). The only negative use I can see clearly is that sometimes I can abuse it when I get very angry at someone. I've read that inferiors tend to be an all or nothing thing, and the all or nothing part of inferior Te that I can clearly see in myself when I'm angry. Insight into people + anger at them = bad.