Do not use registry cleaners. Registry cleaners pick and choose which registry keys to delete, and this leaves gaps in the registry. The kernel time savings in passing over deleted keys is insignificant, and in fact, may take longer. Sometimes the registry cleaners "guess" which keys to delete, and sometimes they delete valid keys, thereby rendering the affected programs corrupt.
Don't use registry cleaners.
Don't use third-party file cleaners. Sometimes the files are completely legitimate and take less than 2% of disk space, the deletion of which is insignificant in disk head operations and file searches. Use only the disk cleanup utilities that comes with Windows, or your operating system. Sometimes, the third-party cleaners also delete valid files, causing corruption in the normal operations flow of your computer, creating far more problems that it solves.
Don't use third-party file cleaners.
Don't use registry cleaners.
If you want to speed up your system because you think it is slow, then run msconfig in the command bar, and see which startup programs you can uncheck so they do not run on startup, each of which cuts into your kernel processing, thereby slowing your system down. Essential background services only on startup, the rest on manual, since they can be run at will after the system has booted. For example, I have only one startup program, and that is DVD play. All others on manual, not loaded at startup. On average, I have 80% of my memory free because of this.
My boot up time from power up to logon screen: 21 seconds, with Windows Vista SP-1. SP-2, after I installed it, only served to slow everything down to where I had to do a clean reinstall with the factory settings, uncheck all unnecessary startup programs, and essential services only. Power down time is about seven to eight seconds. Sleep time is about two seconds. All because I have all unnecessary services on manul, not running in the background, not eating up cycles.
I do not use Norton or McAffee anything. I use only Windows Defender, the firewall and MS security essentials. All scans come up clean. My system has never run faster nor more efficiently.
Do not use registry cleaners.
Do not use third-party disk cleaners.
Defraggler by Piriform is okay, though, I've never had any issues with that.
Windows disk cleanup utility works just fine and only deletes files that knows will not cause any problems or system crashes.
Leave the registry alone unless you know EXACTLY what you are doing.
System slowdowns are not caused by old registry keys from deleted programs, or even old files that aren't used any more, but too many startup programs running in the background you can fix yourself with msconfig from the search bar on the start button (if you have a start button). The program marketers don't tell you this because they want to make money from you and make you think you have an infection, like "1183 issues fixed". LOL. Most of them are non-issues and do more harm than good in removing them.
Don't be fooled. Leave well enough alone. Less is definitely more. Do not overclean.
Now, you are informed. Have a wonderful day!