We didn't at first, but at our organization we had to put CCleaner on the machine at least temporarily, to clean up the mess malware left behind. We controlled a lot of the installing and uninstaling on the network, so their isn't a wholelot for a registry fix to do.
So unless there was a specific problem we never used them either. Like you said, the client was probably not even at their desk or already gone home by the time I did the work on it.
We didn't start using CCleaner until we could get the licensing problems out of the way, and by then it was 2005. I don't know what they use on the contract now.
I like using it for pesky programs that won't remove so you have to delete the file folder in My Programs and you definitely have to fix the registry after something like that if you don't want popups an constant error reports flowing all day.