TBH the cleaner does not touch any of your physical files you have created\saved, and this one is possibly the most recommended cleaner out there, all this cleaner removes is the junk and temp files you don't see, and it also empty's your Recycle Bin as well, so the only possible risk you have is if you have deleted something, then change your mind and want it back (but if this concerns you then uncheck that option, otherwise leave it at the defaults), which would be a rare thing for most people, if I delete something then it's done with, if I am unsure I leave it where it is, simple.
Now you can specify for the most part what it does clean, I always use the default settings, and have never had a problem since I started using it many many years ago, well I have had 1 issue, but not with cleaning the junk, it was with the Registry part of it, this was way back when I first started using it, I had to reinstall, but since then I follow the guide of don't touch the registry full stop, but as a cleaner it's a great program.
The biggest thing you may notice is if you use cookies to stay logged into sites like this, this (and pretty much any cleaner AFAIK) will remove these, so you will need to login again each time after you use it, the good news is if this matters to you, then you can tell it to save the cookies you need, this is easiest done by going to the site(s) while not logged in, run the cleaner and close it (this removes the redundant entries that will only confuse the situation), log into the site touching nothing else.
Then launch the cleaner again, then click on the Advanced tab on the left, then select Cookies, you will see x number of cookies listed, highlight them and move them over to the Protected side using the arrows (do the reverse to remove it if needed), repeat for each site as needed, it may sound a bit of a chore, but you only need to do it the once for each site, and add future sites as you may need, from then on you can clear the junk without having to loose your login being save.