after you do some seo,(backlink or onpage optimzation), when google know it(update the cache), when will your ranking be affected? it seem google tread site individual.oftenly, my site got boost and other site(same niche) got where it was. vice versa. post your experiences here. so that make thing clear.
some changes can affect rankings which also affect traffic... sometimes it affect everything, like a domino... which usually normal... SEs are unpredictable.. you have to make some adjustment, if they make some update/changes...