Power modes and what they affect?

Apr 8, 2013
I was wondering what the different power modes do; I know they affect the amount of active cores, clockspeed and screen brightness, but what else?

Since I started using my Mi-2S whatsapp messages come in very late or not at all, unless I manually open the app. I use power saving mode all day long, unless outside in the sun where I switch to normal mode (to release the screen brightness cap). So I was wondering maybe power saving mode affects background data in some way?

On my old Nexus S whatsapp notifications were always on time like clockwork, even though the thing was starving for RAM. I'm still on the same operator network, so the only thing that has changed is the phone I use.

Does anyone know the details about the three power modes on an M2S?