CCleaner is so good I've seen it as an essential part of my Windows system for many years. But, that means it is also powerful, and if you play around with the settings, it could do serious damage. Since you need to ask the question, I would get it and use it only to delete files, and only those it deletes by default. The registry cleaner is good, but there is no point in using it. Registry is pretty good at cleaning itself and no fine tuning can have any detectable effect on computer speed - contrary to what many software vendors will tell you. Much better to leave the Registry alone. You can also disable startup programs. This is very useful, but I would leave it until you are sure you know what you are doing - although all your actions can be easily reversed so long as you don't delete the software. I generally disable startup entries, watch how it behaves for a couple of weeks, and then leave them disabled. Used just to keep your disk uncluttered, with default setting, CCleaner is safe and very effective. It will make your disk faster and reduce the need to defragment. I do this daily since modern browsers store an awful lot of junk.