Why do different registry cleaners give different results?

First, I need to be up front and let you know that some of the companies that create and sell registry cleaners and optimization programs are occasional direct (i.e. non-Google) advertisers here on Ask Leo!. I say that up front to hopefully avoid concerns that I might be influenced by them, and to allow you to make your own decisions well-informed.

Ads that show up in the Google ad blocks are, largely, out of my control, but I only accept direct advertising from companies that I believe are relatively reputable.

But that doesn't imply that I think that their products are always necessary.

In fact my stance on registry cleaners is pretty clear: 99% of the time I don't think they're needed at all.

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So, why might different registry cleaners return different results?

In short, because there's actually no definition of what it really means for the registry to be "clean".

Oh, there are some obvious things, like perhaps references to files and software that no longer exist. But the bottom line is that the registry is such a complex collection of data that it's nearly impossible to encapsulate all the rules of what can and cannot be cleaned, what's safe to remove and what's not, into a single cleaning program.

This concept of "safe" is also a very important difference. It's not always obvious whether a particular cleaning action will, in fact, be safe and not have unintended side-effects. Many registry cleaners will allow you to specify how "aggressive" they are to be, and others simply select a particular level of what they feel is reasonable.

Neither are wrong, but neither can be completely right either. It's just not that simple.

And it's another source of differences between the different products.

The model of telling you what's wrong for free but then charging you to fix it is, in fact, a legitimate sales approach. Unfortunately it's also abused by various malware and other companies to occasionally scare you into buying things you don't need, or worse, installing malware on your machine.

So how do you tell what's what?

In my opinion it's all about reputation. Do a little research and see what independent (and again, reputable) third party sites report on various tools. See what discussion groups say. Even my article that says that registry cleaners aren't typically needed includes a couple of recommendations.

To further complicate matters, purveyors of malware and disreputable tools appear to be very good at deception. Take care that you aren't reading "planted" testimonials, watch out for "sound-alike" product names, and other scams.

But the bottom line is that as long as you take care to find and use reputable products, and follow their instructions, taking care to always backup first, you should be fine.

Even if the reputable products give different results from each other.