It's wonderful for fused applique or freezer paper applique -- just make sure to use a pressing sheet. I also like it for pressing a quick seam (or getting out a small wrinkle while I'm at my sewing machine. I've found that a 3oz water bottle works great to seam out any wrinkles in the fabric.
The main thing I love about it is that when pressing (1) applique or (2) folded edges (like for a folded star block), I can press without burning my fingers. I have no idea whether a mini iron is useful for most people. I have nerve damage & cannot feel hot or cold, so I was getting blisters all over my fingertips and finally realized I was burning them on the iron. I don't have that problem anymore.
The mini iron with the Large face plate (it's not very large, but that's what it's called) is great for taking to Quilt Alongs or classes for small touch-ups on fabric that I already starched & pressed at home.