i use cutting as a "coping mechanism" - so i do have to say that it can cause some harsh consequences. cutting shallow with a clean blade is safe, but should you take it too far, medical intervention may be necessary.
my experience is being driven to A&E after cutting my lower inner calf with a razor blade. i could not walk on my own. the incision was roughly 1cm wide, 10cm long, and 1cm deep. i was injected multiple times with local anaesthetic, and 5 stitches were required to sew it back up. i was told by the medical team that i had almost severed an artery in my calf, and could've suffered immensely. the stitches caused a major irritation with my skin (an allergic reaction i think), which meant that the wound took several months to heal. i had difficulty walking for a long time, and everybody around me questioned it often. i was required to complete a mental health evaluation immediately afterwards, where they determined i was of medium risk - and an appointment with a mental health professional was scheduled.
i think it's important to highlight the dangers of cutting as well as the benefits.