When I GM, no matter what game, I try to use player involvement as much as I can. All RPGs got player involvement, but when I mean it as a term, I'm thinking of letting the players create stuff on the fly that I as a GM have to adopt to. It may be things in the environment, people they encounter, relationships and even plot things. You will probably recognize this below, but I think I will show it in a slightly different context.
And is something I use to add to the players description. For example when the player describes the characters action or when the player "invent" something in the environment that I feel that I can build on. Using "and" is also a sort of confirmation. I acknowledge what the player is creating, which is a sort of reward. I even use this in a OSR kind of game while fighting, to let the players know how damaged the opponent is. I can add "...and there is pouring blood out of the target's wound", where "blood" is a keyword for "lost half of the hit points".
But restricts what the player just said. By telling the (traditional) players that I can always use "but" to restrict their figment, they get more confidence when it comes to creating things because they don't have to feel that they will break any boundaries. I do point out that they control the silliness of the game. If they want to create unbelievable things then I will adopt, but I will tell them how I usually play the game (realistic, hong kong action, horror et c.).
Because is giving the players something to play with. It gives a reason why something is in a certain way. I usually use this when I say "no" but that's not always the case. By using "no, because" I can still give the players a way around the problem. "No, you can't go through that door because there is guards there". I can also use it if the player creates something that I want to give an explanation to. "...because it's part of their religion".
Here's the thing. I'm not the only one who may use these three words. I encourage the players to use them to build on the others players narrations. By doing this, having the players create a dialogue within themselves, I kind of remove my part all together sometimes. The players can go on building a story, adding or restricting things from each others creations and even create adversaries to fight. The only thing I do is to add more wood to the fire if I feel the flame is fading. By letting the players taking chunks out of the normal GM role, I reduce the amount of work that I have to put into my role in the game. Only once, of the last 15 sessions (a 1-2 hours of play) with total strangers, have I been forced so say "No, that doesn't work. You have to come up with something else".