A lot of the people using them mention killing the ego, I've never done anything like that and wonder what do you think under the word ego? I know the literal term obviously.
As an example: given that you have free will, at any moment you could say to yourself, "hey, there are X and Y habits/traits I have, let's not do those anymore and do Z instead." Maybe it's smoking, eating badly, you don't treat people the way they deserve, being a doormat, whatever. You could absolutely choose to become an entirely different person overnight. You might also change your career/lifestyle overnight (not everyone is so lucky though).
Now the ego swoops in and says, "Hold on, let's not do anything crazy, it'll be scary and embarrassing if I suddenly act differently, what will my friends think? It's easier to keep on keeping on. These habits are just things that I would do. It's okay when I do these things because I'm me." and so on like this.
It's helpful to be able to experience the world without the influence of the ego, because then you are able to experience the world in a completely unfiltered way. You are able to get closer to an experience of objective truth.
Many people who have used psychedelics or work deeply with meditation all come to similar conclusions: the ego is an illusion. All beings are one and the same. Your sense of "separateness" from every living thing on this planet is a function of your ego-filter — and your ego-filter is wrong.
It's strikingly similar to death experiences I've had slowly waking up as I die in morning dreams ...