I have everything possible made into a portable app to keep the system clean, avoid re-installation and so I know where everything is to do with each app. Portable apps only use resources when running, unless it's told to do otherwise for some reason dependant on the app.
That's one of the bonuses of portable software that many users don't see. Admittedly it's only negligible, but add the other 20 or so negligible additions and you have a fair amount of resource hogging going on.
One installation is all that's needed and it doesn't add to the bloating of system resources causing issues for those with less powerful systems. I help out several people with PC issues and constantly installing software is a pain in the ass! Having a portable version saves a lot of time and hassle. Your idea of keeping the install file on a USB drive is fine, if you don't mind installing every time you want to use it on a different computer! For me the whole point of portable software is to stop the need to reinstall everything and set it up how I want on a fresh Winstall.
