I like backing up my text messages and Gchat logs - there’s a lot of sentimental (and sometimes work) value.
In the past, I’ve had these on different platforms - Gchat was in my Gmail window, Facebook chat (when I rarely used it) in Facebook, and iMessage on my phone.
I’ve spent a few weekend project days trying to get them all into one centralized, plain-text archive, but have always been frustrated in one way or another, from weird JSONy Google exports to the general hairiness of iMessage and getting anything off your iPhone in a suable format.
Mac Messages is huge for me because it brings all of those platforms onto my desktop, and saves them locally. From there, it was just a matter of linking a copy of my local folder to a Dropbox folder, and ta-da:
> ln -s ~/Library/Containers/com.apple.iChat/Data/Library/Messages/Archive ~/Dropbox/chatlogs