I don't think it's a bug, most programs use this area to store user data for applications and iClone is not the only program that doesn't delete AppData folders even when uninstalled, DAZ is the same way on my machine as well as Adobe and Apple's uninstallers.
However it could actually store a corrupt file which is what I'm assuming happened when I was having issues with iClone after the last patch. Uninstalled/reinstalled several times and still had the exact same problems with every re-installation, only after finding the iClone AppData folder and deleting it did all the issues with reinstalling and consistent hanging disappear.
So I don't think it will hurt anything to delete it if your having problems, it will put it back as it's supposed to when needed. Most disk cleaners can be run automatically at start up or shut down and should let you specify folders or files to include in it's scan.
For me personally I'll leave it alone as long as the program is playing nice with me and if not out it goes before I spend a week or two back and forth with support to try to figure out why the program is having issues, deleting the corresponding AppData folder will be my first step from now on.
Dell XPS 8900, Intel(R) Core(TM) i7-6700 CPU @ 3.40GHz, 3408 Mhz, 4 Core(s), 8 Logical Processor(s), 16 GB RAM, - 4 GB GeForce GTX 745, NVIDIA compatible.
Acer Aspire V Nitro Laptop, 2.5GHz Intel Core i5-7300HQ processor with 6MB cache, 256GB solid state drive, 16GB Ram, 4 GB NVIDIA GeForce GTX 1050 Ti graphics.