Use portable applications to keep your Windows clean?

Hi everyone,

I'm new to portable applications. As far as I know, portable applications can run from an external usb drive, and they do not need to be installed. Does this mean using them can keep Windows clean and fast?

Well, the truth is, every Windows version (XP, Vista or even 7) is super fast and clean at the first times you use them (after installation). However, over time, when you install more and more apps on your computer, the OS gets slower and slower, largely due to the expanding of the applications. They consume disk space, they leave junk in the registry etc. So I am considering the possibility of switching to using portable apps, as much as possible, to overcome this issue.

How do you think about that?

Thanks in advance!