I tried to use it to tack 1/4" rick-rack to my quilt while I sewed it down, but it didn't hold. Just made a colossal mess. I have used it to temporarily hem pants & also to make fabric covered boxes. I would say, in my experience, it works best when bonding fabric with something other than fabric (e.g., if you want to frame a piece of fabric, you could use Fabric Fusion to adhere fabric to cardboard; covered boxes; fabric-covered Christmas ornaments).
I've found that it tends to be slightly visible through the fabric when you use it to glue fabric-to-fabric, makes a mess & doesn't give smooth results unless you use an offset spatula to smear it across the fabric evenly like frosting a cake.
If you want something permanent for fusing fabric to fabric, I suggest WonderUnder. The only time I'd use Fabric Fusion for fabric-to-fabric application anymore would be for a heavy weight pant hem (like jeans) where some of the double-sided fabric tapes aren't secure enough.