Yes it is - i clear up after all of my pieces.
For the ZIFTER one I actually had to leave almost as soon as i was done, but I came on half an hour later and my friends told me that people came and picked up all the pies within minuits ^^ but since i dropped about 100 pies in hydlaa i guess it did lagg up the server for about an hour...
I did try and ask GMs if i was allowed to but none of them were responding on IRC... After I did it I told them and they said that because I [people] cleared up after it was OK. But if everyone started doing it it would not be allowed...
. But some GMs [Mord] think that its a complete waste of time and is completely against the rules... So I guess it depends on who you ask.