during the early testing/deployment stage there have been quite a few collections and advertisements created for computers in the lab. I am just wondering whether I can delete some of the advertisements that have been completed and those associsted collections? If I do so will the deleted advertisements be removed from client computers automatically? Thanks

Any software that was installed will not be removed automatically after the advertisement or package was deleted. So it's safe to delete them without having effects on existing clients.Torsten Meringer | http://www.mssccmfaq.de

Hello - Yes, to speed up the process you can run the machine policy retrieval and evaluation cycle in the Configmgr client (in control panel) on the client.Anoop C Nair

And the same goes for the collections. Actually, if you delete a collection, all advertisements associated with it will also be deleted. Before you delete a collection you can open it's property page and look at the advertisements tab to make sure there aren't any other advertisement to the same collection.