Picking up a message part way through a thread without the context of
earlier posts can be a bit difficult (and surreal) at times. I fully
accept Peter's point that some prefer not to received a screed of
earlier messages, but there are solutions to this both for the sender
and the recipient. Most e-mail clients allow the sender to set whether
his message includes the message to which he is replying. For the
recipient it may be possible (certainly it is in Thunderbird with a
couple of extensions: QuoteCollapse and NestedQuote Remover) to collapse
ALL earlier messages in a thread to just a couple of lines).
Actually I have just realised that the main reason my posts appear to you all as disjointed ramblings is that my Cix mail client does message threading by default and does not include the original message, whereas with Outlook you have a setting to include the original message by default to keep the sense.
I knew there was a good reason why I have never used Outlook except when forced to at a client' site. Plus Cix's address book is not easily hackable as it is encrypted.