I believe the list of apps shown when holding down the home button is the recently used apps, not currently running apps. In a nutshell, when an app is not being used Android could close the app to regain the resources. With 2GB of RAM, that probably won't happen too often if you switch between apps quickly, but technically it could.
The Slide Aside feature might ensure the app stays on memory. I don't know if out actually does that, but of it did that would be one way i could see it being useful.
I thought Slide Aside sounded really cool when i first heard about it, but to be honest I've never used it after the first day with the phone. The recently used apps list works good enough (and easier) for me.