If I get a noice that CCleaner can save 1.5 GB, I might think that is significant enough to interrupt my work and run CCleaner. After a long while of "analyzing" and "cleaning" CCleaner reports it has saved about 3MB. Sometimes less than 1MB. I have seen the "save x GB", closed everything, restarted my computer and ran CCleaner before anything else, and get the "saved xxx MB" instead of the 1.5 GB the notice said it could save.
This is very annoying. If it were going to save the x GB it would be worth the time, but since it didn't it was just a waste of my time.
Also, besides the annoyance Itry not to run it at all because when I do even though I have explicitly told it to leave my filezilla saved information alone it deletes my stored username and password for the only FTP site I use.
I have gone from "loving" to "kind of like" to "I'll run it if absolutely have to" and while I won't exactly un-install it I will turn off the notifications, since they are obvious lies.