My favorite about Heavy Body acrylics is that it's flexible when dry. You I use heavy body acrylics in my nail art and my decoden if that helps with an example. Probably not but I can't think of a better example right now.
Heavy Body also tends to paint like oil paints. It's nice to have a few in your arsenal if you want to try some oil painting techniques without the dangers of oil paints & the clean up. Remember it won't be exactly the same but close. My DH does oil painting and he switched over to Acrylics recently.
Many years ago I used heavy body acrylics in Printmaking. I have not done that in years though. I don't know if that is still the trend or even taught in classes.
My big paper love is collages. I am a massive collage junkie. Heavy body acrylics are loved by collage artists. It's a wow factor in collaging.
Already mentioned is Impasto. Heavy Body acrylics are a must if you want to work with Impasto or other paint knife techniques.
I keep a few colors in my acrylic toolbox. It is fun to work with. They are a bit expensive so it is an investment. They do last a long time with good care.
Hope that helps.