Deletions are usually done to clean things up so ppl using the search feature arent discouraged and/or the posts/threads are a monumental waste of space. Times when i prolly wont send a pm that a post of someone's has been deleted:
When i delete an old thread cause its been repeated a bazillion times since with nothing new added (like: how do i register a nick, dcc pending)
When i delete 14 nonsense posts from a thread saying
ksjghwerio or
or absurd bickering (recent example: 16 posts arguing whether fish is a meat or not) or extremely unpleasant, disgusting or incorrect
When someone is spamming or asking for a specific movie,crack, intending to only be annoying etc and i send them a pm about it instead of posting a reply, other replies telling the person not to do whatever they did go with it
When someone makes a post that HAS to be edited for content or completely deleted and the next 10 ppl feel the need to include a quote of that content in their reply telling the person they are a twit.
Offtopic: well, kinda depends. Are they a progression of thought from the original post or are they a ton of "gee im bored" "so am i" "why do bananas grow on trees" "you're stupid" "no, you are"
I see no need for a "manure pile". If they werent worth reading once, why keep them? Besides, they would just be flame fuel.
