That is not true... programs are just going to take up space on my HDD until they are used. A total of 20GB of seldom used space isn't going to make your computer run worse then if you had 20GB of empty space (not when you have 500GB...). Some programs may try to stay running all the time by default, but that is usually easy to fix.
Also, I only download stuff that I know I will use. So if you know that you will use it, but you don't download until you need to, then you are costing yourself time when you finally do need to use it. That can be much more harmful then the alternative.
I have personally kept my computers clean and efficient for years. Plus I have done more then my fare share cleaning other people's computers to help them run like new again.
Can you elaborate on your opinion?
the HDD space has nothing to do with it. Years ago when it cost a kidney to have a drive with a two figure capacity on it, maybe so, but today its irrelevant.
The more stuff you install the more information it adds to the registry. Bigger registries lead to more bloat which means it can take longer to find information. Don't forget when you install and uninstall stuff it doesn't totally disappear, registry entries, temporary files, empty folders, working access folder, get left behind clogging up the file tables, clogging up the registry and just sitting there doing nothing.
PCs are like cars - If you know you're going to be the only person inside the car the vast majority of the time, you don't go and buy a people carrier do you? Likewise if you know you'll only use that Microsoft Access program once a year for your job and you routinely wipe the system every six months, its pointless installing Access during the six months when you don't need it isn't it?