Having a bunch of extensions installed in Chrome and make Chrome lag. Do Chrome Apps have the same effect or do they only affect Chrome when they are running?
the difference between "apps" and "extensions" is that your extensions are active whenever ONE page is active. "apps" are only active, when you use them. if you activate them, they become a new tab and thus a new process.
you can check the current memory / cpu - usage by pressing shiftesc to bring up chrome's task manager.
They act like a tab because of how Chrom(e/ium) is built.
The Chrome browsers are built to be modular in nature, each tab is it's own process. This is both good and bad, good because you can move tabs around without them reloading like in Firefox and bad because it means their taking up a bit more processing power.