In the old days of Minecraft modding you would boot up your modded world and be greeted by dozens of messages in chat, various books, guides and all sorts of starting items - as a first impression having so much content thrown at you immediately was rather overwhelming!
Thankfully those days are long behind us, but some mods still drop a book or message on first load. I'd just like to suggest turning the config option off by default to help combat "mod clutter", thanks!