Ugh, I really hope i would never have to deal with this power. ;-; But if I did, and i had the power to suppress it, I would. Forever. i would not want that on my conscience, because no matter how evil or horrendous that person may be, it isn't up to me to do that to them without a proper trial.
If I COULDN'T suppress it though, and I was forced to kill people, i would only kill people who were probably minutes from death anyways, like people who were a hundred and twenty year and suddenly in the midst of a heart attack. I would just end it before the heart attack could, so I wouldn't feel as bad, since they were more than likely going to die anyway. (Of course, I would feel really bad if it turned out they would have survived. ;_; Hence why I would wish to suppress it or not have it to begin with.)