I've introduced a character questionnaire for my LARP since I've found that most players (myself included) often have enough of an idea about their characters to be reactive but not enough to be good conversationalists. Oftentimes someone will ask a question and get a very superficial response because you haven't really thought about it.
Now while you can sometimes come up with something off-the-cuff it becomes more difficult if it involves history, work details or occultism you didn't research. It also makes you less likely to ask certain questions that you don't know the answer for which cuts back on a lot of potential LARP conversations and means that what history you do have may well sit silent and unseen in your memory.
So I created a set of questions and offered a pretty substantial amount of free XP for those who complete it but taking another look at the questions I realised that those who slavishly follow them in all of their permutations may well end up with a massive document that doesn't touch on what I need to know.
Having helped a few players through it I've found that these questionnaires are better asked, developed and queried by another person. In that way I can ask the main questions and then ask a few more clarifying questions depending on the player's answers. If the player's answer mostly covers the detail or signals a greater understanding of that detail, then we can move on or use another permutation of the question to tease out further details.
So I would recommend that those who do character questionnaires sit down in pairs and read it out to each other or get the Storyteller to ask them and record the answers. The human element also makes the whole enterprise a lot more fun and can get a player to look at things in a somewhat different way.