The internet is a two way communication system.
Most of the programs you install in your computer are designed to check the whole information in your computer. Even your phone company can pull whatever you have in your cell phone, from passwords, pictures, documents, etc.
These companies won't "steal" your information or use it for gain, but they will know all your privacy.
Every new program you put by download means, will open new viewers of your internal computer system. So beware of the free programs assumed to help you clean your computer, they must send you viruses and malware. You can do the same cleaning by following the tools that every computer has to do so.
Also, going to control panel you can uninstall every program that is not useful.
On the other hand, when a company does it for you, the company can copy everything you have in your computer, and you can't impede it and you'll never noticed it.
There is lot of help online to make your computer running properly, and avoid the dudes suggesting to download a certain software as the first step. First choice must be the computer brand technical support and the anti-virus company you use. They have the proper tools to clean up your computer.
Of course, they will also pull your information, but you don't have to worry about it, because they do it anyway each time you accept their updates...