Android 4.2.1 - Background processes keep running :(

Hi
I need some information regarding Android. I am using Huawei Ascend G610-U20 with Android version 4.2.1
I was using stock ROM and stock theme. No launcher installed and no themes used. When i touch and hold the menu button (one of three main buttons, return-home-menu) i am given the list of applications running in background. I quit the application which i am not using so that it doesn't hog in memory and keep eating the battery. I only keep phone and text in use. Otherwise once i have used the app, i exit it from the background running processes.
Recently i installed Dodol launcher. It is running fine and nothing wrong. Just when i press-hold menu button i see no applications running in background (because i have exited all the apps from background) but when i go to launcher and click "running" apps it shows me a huge list of apps running in background. I click on broom icon to clear them. It does but they again appear after few moments. They keep using the RAM. SOMETIMES my phone become too sluggish when i am typing in Viber or even Text app.

Why is this difference? That i exit the app from menu-hold but in launcher it shows apps running. Can anyone please guide me.
I will be very thankful to you.

Regards
Awais.

 

Thanks for the kind reply but whats the purpose of viber or whatsapp or camera app running itself in the background even though i have killed it's process.
facebook
messenger
settings
twitter
youtube
sim card tool kit

All of these are running in the background even though i have never used the youtube app ever.