The trouble with saving all your chats is the sheer volume! I used to keep all my text messages, and log all my IM conversations. Until I realized I had 2,000 text messages on my phone, mostly worthless out of context, and megabytes and megabytes of IM chats. Unless you triage your conversations regularly, logging everything just results in a gigantic mess you will never revisit due to the stunning volume of your archives.