[TeHCrAzY]

There is a significant effect from account deletion. You are removing some of the motivation of your friends to interact with the web site. My account deletion had a significant effect within my social group, as I was a moderately heavy user. When I left, the "pull" from my comments and interactions ceased, and peoples usages of the site decreased considerably. (Confirmed via my girlfriends account, which lives in a very similar part of the social graph).