Dear Aunt TUAW,
Ever since I started using Messages, it appears to be logging everything it does. Can this be disabled, or can the log file be moved to somewhere out of the ~/Documents folder?
Your darling nephew Tommy
Auntie's tending to the spring turnover of the vegetable garden, so she asked Uncle Mike to chime in on this question. The beta of Messages, like its predecessor iChat, has a feature that automatically saves chat transcripts (including transferred files or images, which can get out of control pretty quickly if you're not minding it).
Unlike iChat's setting, however, in Messages there's no way to turn the logging off. Be sure to let Apple know that you'd like to see this changed before Mountain Lion ships!
With regard to the second half of your question, the answer is absolutely yes; you can go into Messages' preferences, click the Messages icon in the top bar, and then adjust the "Save chat transcripts to:" folder however you like.
Since you can't disable the logs, the next best thing would be a way to clear them out periodically -- once an hour, once a day, once a week, whatever. There are scores of approaches to scheduling repeating tasks on your Mac, ranging from the UNIX-savvy one-liners (cron, launchd etc.) to capable and flexible commercial applications (Auntie's terribly fond of Noodlesoft's Hazel). For something like this, though, if you want to clear out the logs once a week, you might give OS X's built-in Automator utility a try.
Automator lets you set up a workflow to run when triggered by an iCal event, so it's straightforward to set up a repeating "silent reminder" that simply goes into the logs folder, grabs what's there and tosses it into the Trash. Here's what the workflow would look like:
Each step in the workflow passes its results along to the next step, letting us zero in on what we actually want to throw out. This workflow starts by identifying a specific folder (in this case, the iChats log folder), then getting the contents of that folder, and finally moving those items to the Trash.
When you save an iCal alarm workflow, it gets dropped right into your calendar. You can then adjust the repeating schedule to make it run at whatever frequency you like.
The log files will end up neatly in the Trash; no muss, no fuss... which is more than Uncle Mike can say for Auntie's rows of sugar snap peas. This same technique can be used for any folder that tends to accumulate things you don't actually need to keep.