There are a few cleaning addons, but none clean everything. Some are not maintained and all functions don't work. So I ended up using 3 different cleaning addons. And then I decided to write my own, and add a few things no other cleaning addon has.
For the time being, it cleans: Temp/Cache, Packages, Thumbnails, ATV downloaded files, Addons
There are 9 addons which are cleaned, I tried to find ones that collect the most garbage, temporary files, or just a lot of files over time. These include some that might actually be useful like "ArtistSlideshow" that collects a lot of images. If you need these images, then don't run the Addon cleanup - but anyways they would be downloaded again, so they can be considered cache files.
If you have device that is running low on space, cleaning all the downloaded stuff and cache with a single press can be useful - and about the only option you have!
The list of supported addons: WTF, 4oD, BBC iPlayer, Simple Downloader, ITV, MP3 Streams, ArtistSlideshow, Titlovi, Titulky. Latest version can also check if you have any repositories installed that are unnecessary because you don't have any addons from these repositories and you can uninstall them.
You can run any section separately or everythng at once. At the end you will get report with stats how much Mb was recovered and what was cleaned/checked.