Facebook timeline privacy question?

[way2play]

hey all so i got timeline and i want to make sure 100% only friends get to see my posts, etc. and try to make everything as private as i can.

my question is about this one privacy custom setting im confused about, it says this:

Limit the audience for posts you shared with friends of friends or Public.

Should I limit the audience to just friends? When I triedt o change it it warned me saying that if I confirm there will be a global change and that i would have to change every post manually for my audiences. Why is it warning me? Should I still go along with it? It seems like fb is trying to intentionally change my mind so that MY PROFILE IS MORE VISIBLE TO ANYONE.