KDE4 Activities - What can they do today?

How are Activities in 11.2 KDE 4.3.5 nowadays?

Can they simulate sessions?

KDE Activities are a mystery to me. When I experiment with them in Suse 11.1, it often destroyed various KDE settings and hence I stopped trying. From what I found on the Web, Activities just let you define different sets of Desktop-Widgets and Wallpapers. And that is it?

When I reboot, KDE restores the previous session, i.e. opens Applications and places them as they were before. Can Activities simulate this to, i.e. allowing me to have multiple sessions and switching between them?

AFAIK if you set up an activity and then logout, it will be restored in the same way as KDE normally restores the session. Activities are just a different way of organising work.