Depends, some people use it as a diary just so they can keep track, others ask for advice on what they're doing right/wrong, others use it as a bit of a social chat thread, others use it to post ideas on recipes they thought were nice that other people might want to try. All sorts of reasons.
If you want to start a diary just start one in here in your name, then if you want to ask for advice on it just post a link to it in the other main room asking for people to go look at it and help you out.