I personally like to charge 1L for demos because it's easier to keep track of who is buying what. I tend to skip over 0L transactions in my history so if I see 1L it grabs my attention. Dunno about Pita tho!
Not really sure about the train of thought for people who charge 10L but not alot of people do that I know of. But yeah I think it's really more for keeping track of transactions when they charge 1L.