It's also a form of 'auto-hypnosis' and, from my point of view, potentially dangerous, which is why, for the most part, I got out of auto-hypnosis many moon ago
Believe it or not, even telling yourself 'every day, in every way, I'm getting better and better' can be a problem...
Since, sometimes, it's not true
Just about everything is potentially dangerous. I could get bitten by a poisonous spider while I sleep but that doesn't prevent me from going to bed at night. I could smash my thumb with a hammer but that doesn't prevent me from using one to hang pictures or build something.
Affirmations are a tool for directing your focus and/or changing beliefs that don't serve you, in order to experience more of the things you WANT to experience, so, when you are using an affirmation it is often because it is not true (yet) but you would like it to be. Telling yourself 'every day, in every way, I'm getting better and better' would not be effective if you were unable to find any aspect of that statement that was true for you because then the only thing you would most likely be focusing on, and therefore attracting more of, would be how totally 'un-better' you are!