If he's from an Android platform, he will probably won't very much agree with your explanation. But yes OP, you do not really need to care about closing up or should I say kill, apps you open. 2 great benefit of it is that it use less battery when relaunching the apps that are already in the background, and second benefit, it launch much faster than if it was kill completely from the back ground.
Some apps I the background can continue to be running though, causing some usage of battery and even some usage of data, that is if your ipad is a 3G, apps like skype and apps like one checking for your location constantly. To prevent those apps to be running in the background causing extrem battery usage and sometime data usage too, go to settings> Privacy> Location service/ there you can prevent some apps of performing location update and stuff related to location service.
Also go to settings> general> background apps refresh/ there you can prevent some apps of running still in the background.
Sent from my iPad using Tapatalk HD