While an article about registry cleaners may appear somewhat incongruous in a channel dedicated to security matters, it actually fits extremely well. Security is all about protecting data and ensuring availability and registry cleaners - sometimes called registry boosters - can impact either or both.
According to Wikipedia, “The Windows registry is a directory which stores settings and options for the operating system for Microsoft Windows 32-bit versions, 64-bit versions and Windows Mobile. It contains information and settings for all the hardware, operating system software, most non-operating system software, users, preferences of the PC, etc.”
In all versions of Windows, the registry accumulates old and obsolete entries which are the result of, for example, bits and pieces being left behind when a program is uninstalled. Registry cleaners delete these old and obsolete entries and in doing so can enhance performance and remedy application and operating system errors. Or rather, that is what the vendors of these products claim. In reality, however, registry cleaners have an extremely thin set of benefits but a substantial set of risks.
Firstly, let’s examine claims that a registry booster can enhance performance (“Without the need for expensive hardware upgrades!”, according to one vendor). The registry is designed to hold extremely large amounts of data and an accumulation of old an obsolete entries will have practically zero impact on a computer's speed. According to Mark Russinovich, a Technical Fellow in the Platform and Services Division at Microsoft, “Even if the registry was massively bloated there would be little impact on the performance of anything other than exhaustive searches.” Certainly, I have never seen any empirical evidence to support claims that registry cleaning can substantially improve speed and, should anybody be able to provide such evidence, I’ll be more than willing to eat my cat. Nor have I ever seen any studies by the vendors of registry cleaners which demonstrate that their products can boost performance. Think about it: programs such as SpywareBlaster create thousands of registry entries without causing systems to slow. Similarly, with hard disks now coming in GB or even TB sizes, most of us have substantially more programs installed than we did when drives were a few hundred MBs in size - and more programs equals more registry entries. But are our computers getting slower and slower as a result? Nope. Realistically, culling some obsolete entries isn't going to make a scrap of difference to a computer's performance.
So, what about claims that registry cleaners can cure application and operating system errors? Yes, in some very limited circumstances, a registry cleaner may indeed be able to remedy an error. But it is just as likely - possibly even more likely - that it will cause problems. For example, running Microsoft’s RegClean can break Microsoft Office applications (note that, although Microsoft has abandoned RegClean, it can still be downloaded from numerous non-Microsoft websites). While this is an example of an older and outdated cleaner causing problems, newer cleaners are equally likely to break applications and/or the operating system. There are simply too many variables for a cleaner to be able to be both effective and safe. Search the internet and you’ll find far more reports of cleaners causing problems than fixing them. In the majority of cases, the problems can easily be repaired, but those repairs take time and time is money. Should your computer have a problem that you suspect is registry-related, the best option is to research the issue and, if appropriate, use the Windows Registry Editor to manually make the necessary changes.
Given that registry cleaning will result in an imperceptibly small performance gain (or, more likely, no gain whatsoever), is it really worth the risk? In my opinion, no, absolutely not. Should you use a cleaner on a regular basis, then sooner or later you’ll find yourself expending your time attempting to remedy a self-inflicted problem.
Note too that there are numerous rogue registry cleaners available. See Microsoft Security MVP Donna Buenaventura's article Beware of Rogue Programs: Fake Malware Scanners and Registry Cleaners for more details. So if you absolutely must use one of these programs, be sure to choose carefully.