I would say that "to be honest" means that the speaker is about to admit something he or she would rather not admit or has not admitted previously. It is similar to saying "I would like to lie about this, but instead I am telling the truth," but without making the speaker seem dishonest.

Both "to be honest" and "basically" are filler words that people use when they are thinking what to say next,and they don't really have any meaning.Other examples are "kind of","sort of " and "actually" .People just use them to add to the sentence.

'To be honest' and 'basically' are just 'fillers' which we use to emphasise what we want to say, help the conversation flow, and give us time to think. They have no meaning. In a written context, people use them to make their letters seem more personal, conversational and 'chatty'.

To the extent that it means anything... it COULD mean that the speaker was about to say something slightly less honest, then changed his mind while speaking, and said something more honest. This could be true if the words following "to be honest" meant something mildly embarrassing or unpleasant. Here is an example where the words "to be honest" would not just be filler. The speaker is embarrassed to admit the real reason why he changed jobs. He has it in his mind that he is going to say this: "I changed jobs because I did not fit well with the corporate culture at Megacorp and thought there would be more stimulating challenges at Teratology Inc." But then he realizes he realizes he is talking to a friend he can confide in, and says, "I changed jobs because I did not fit well with the corporate culture at Megacorp and, well, to be honest, I screwed up and was fired."