Coincidentally, they are very good for correcting posture issues like your monkey butt.
I tend to be barefoot most of the day these days anyway (working from home...) so it's hard for me to tell how much they help, but if you are mostly wearing regular heeled shoes all day, you will probably find that switching to no-heels alone will make a huge difference. People make all kinds of claims for them curing back pain and such. A lot of which is probably bullshit but anyway, worth a shot.