This is a really good question, and something I have been wrestling with recently.
The answer changes depending on your timescale; the lower the time-frame, the smaller the traded movements, the more sensitive you are to news. 'Impact' is also just an opinion, and it is not unusual to see different calendars give different ratings to the same news events, and I have been bouncing between a few different calendars, trying to find one I trust.
For me, on the H1, I have found that most high impact events are best avoided, but you have some leeway with isolated medium impact events. I don't even bother checking for low impact news these days.