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I've used CCleaner in the past, and I've never been particularly impressed by it. However, tools evolve, and I was curious to see how much this one had changed, so I gave it another try. It's better than it used to be, but this time I paid close attention to its registry cleaning feature.
After running the registry scan, I sat down and investigated every result category it flagged. If I were to go back to using CCleaner, I'd be skipping the registry cleanup.
254 entries, 0.00 megabytes
What a dedicated registry scan on my PC actually turned up
I ran CCleaner's general cleanup first, and the results were satisfactory (better than I would've said a few years ago). So I took it a step further by unselecting junk and browser cleaning entries, allowing a complete registry scan to run.
The results revealed 254 entries, but when I investigated to see how much space it reclaimed, I found 0.00MB. Don't take this as a rounding error, since registry entries really don't offer opportunities to free up space the way you'd expect your Downloads folder to. These entries are keys and string values sitting inside registry hives. There were no bytes to free, so deleting even as many as 254 doesn't move the needle.
These are the 254 entries I got, broken down by category:
The question the results led me to was this: if none of this is freeing up space, and none of it is a file Windows has to sift through, what exactly is a registry cleaner cleaning? To find out, I had to dig through all the categories.
None of these categories affect speed
What CCleaner's nine registry categories are actually built to catch
Looking through this categorization, I got a clearer picture quickly. Application Paths, Installers, and Obsolete Software are typically pointing to things that may be left behind after uninstalling an application from the computer. They help Windows associate applications with their locations and actions, but stale entries don't meaningfully slow down modern systems.
MUI Cache and Missing Shared DLLs were more relevant when Windows would delete a DLL only after tracking down all the programs that were using the DLL. In modern systems, this mechanism is rarely touched, and Windows has evolved and no longer relies on MUI Cache and Missing Shared DLL tracking/cleanup. Even after cleaning the cache, no process becomes faster because nothing was reading from it in the first place.
Invalid file extensions and Open with Application are connected with behavior after double-clicking a file. This, again, has nothing to do with speed. If you remove the wrong one, double-click behavior becomes unpredictable, but removing the right one, at best, changes nothing.
The two I'll pay attention to are Firewall Rules and Windows Services. They don't slow anything down, but they're not cosmetic either. Firewall rules control whether specific apps can access the internet, and service entries define how Windows manages installed services, including their startup configuration. Both features will change how services or apps behave if you get them wrong.
Looking through all the categories and entries, I could not find one that affected how quickly Windows opens a program, boots up, or responds when you click something.
Clean can still mean broken
The registry entries it removes may not actually be useless
Registry cleaners use rules to decide what looks unnecessary, but those decisions aren't guarantees. CCleaner, for instance, doesn't know the exact ways all the apps on a device use every key it finds. It decides an item is safe to remove by matching it against a list of patterns.
Many of these guesses are harmless. However, even though an Open with Application entry looks abandoned, it may determine how Windows handles a file type you use often. An orphaned-looking firewall rule might be essential for a specific legacy application to communicate with the internet. A misidentified Windows Services entry can be essential to how a process launches at boot.
CCleaner provides an option to back up before deleting. However, backing up a single key is less robust than creating a system restore point. It becomes considerably harder to recover the removed entry if you skip that step.
Microsoft has been wise never to recommend registry cleanup as a maintenance routine. Considering that the scan reveals 0.00MB of space recovery, it becomes clear that you're taking a small risk for a reward that really isn't there.
The tab I've stopped clicking
CCleaner seems better than it was several years ago. It has other features that deliver measurable benefits, like its temp file cleanup, browser cache clearing, and its uninstaller. However, the same can't be said of the Registry tab. Alternatives exist, such as FluentCleaner, but any tool that modifies registry entries carries the same basic risks.
When you have to touch the registry, ensure you're fixing one specific problem. It shouldn't be something you do as a Saturday chore.
