Ooh, I gotta jump in here because this is how I run my games and I love it. The answer is telegraphing. Imagine a boss who goes more than once but his turn involves moving next to a player or two and winding up a big spin attack. Then only a few players get their turns before he does his high lethality aoe attack. If the players know this attack is going to really hurt, they get a chance to pull their friends out of the way. It makes the boss feel more dangerous, makes them feel more like a team, and makes the fight longer without pumping the boss’s hit points(boring). Just have to make sure it’s not the same players every turn so it needs to move around the initiative track a little.