It depends on the app. Sometimes, even if you don't click on it, some apps will run in the background when there is a "call". Like maps, market. etc. will automatically run when you connect to the internet. Dungeon hunter automatically runs in the background when a text message comes in. (I know that is weird!?)
Some apps will even just run on itself despite there is no "call". Some will re-run on itself even if you have task killed it already. Depends on the app how it was written and its dependencies actually. I use a task killer just to know which app does that. Then decide if I really wanted to keep or uninstall it permanently.
And I do move some of my apps to system to save space. I use titanium backup to convert most used "user apps" (usually apps that need to be in internal like widgets, etc.) to "system apps".
Some apps will even just run on itself despite there is no "call". Some will re-run on itself even if you have task killed it already. Depends on the app how it was written and its dependencies actually. I use a task killer just to know which app does that. Then decide if I really wanted to keep or uninstall it permanently.
And I do move some of my apps to system to save space. I use titanium backup to convert most used "user apps" (usually apps that need to be in internal like widgets, etc.) to "system apps".
