The reason you have heard of Bruce Campbell, and the reason director Sam Raimi (Spider-Man) has a career, is that in 1981 Raimi and producer Rob Tapert decided to make a zero-budget horror film called The Evil Dead.
They went into the project without a really solid understanding of how to make movies, and certainly didn't know how to make one full of crazy stunts and gore in a way that was safe at all. For one, all of that fancy safety shyt is expensive -- it costs a lot more to create the illusion that actors are in danger than to put them in actual danger and just film that. For another, they seemed to think the danger was a necessary element. Josh Becker, who worked on the crew, explained in an interview that Sam Raimi would tell his cast, "If everyone was in extreme pain and misery, that would translate into a horror." No one bothered to correct him on this or to explain what "acting" and "fiction" are, so The Evil Dead shot for over a year in which Raimi and Tapert deliberately tortured the cast. How else would the film capture its gritty sense of slice-of-life realism?
So, for a take that required the camera to smash through a window pane toward one of the lead actresses, they saw no other way of doing it than to just smash an actual window. When you see the actress shielding her head in that shot, it's because she doesn't want it to be sliced open by the actual shards of glass flying at her face.
Keep in mind, all of this was happening in a rented a cabin out in the woods with no running water and no heat (they had to wash their hands with scalding hot water from the coffee maker) over the course of 15 months. At one point Bruce Campbell sprained his ankle, and for the next two weeks, Sam Raimi and Rob Tapert would poke at it with sticks to ensure that he kept limping in every scene.
But arguably the most dangerous moment of the entire shoot was the scene in which Bruce Campbell had to fight off a possessed woman who was trying to stab him with a dagger. The trouble was that the contact lenses they used for that iconic possessed look were completely opaque.
So the actress who was supposed to attack him was effectively blind. Oh, and the dagger? It was real. So while the actress' job was to run in Bruce Campbell's general direction, swinging the dagger out in front of her, his job was to not die. If that scene in the movie seems more real than any others, it's because he is legitimately trying to avoid being stabbed.
It's not entirely clear why they were so insistent on using a real blade, but Rob Tapert has a very telling quote on how he feels about actors. After one of the actresses cut her feet to shreds during a bare-footed running scene in the woods, he noticed the blood tracks and said, "I like it when an actor bleeds. It makes me feel like I got my money's worth."
Granted, the budget of that entire movie was less than $400,000, so the actors were probably getting paid in Sizzler coupons, but hey, that's worth bleeding for, right?