I don't really agree or disagree - I guess it depends on your situation.

I haven't written out a birth plan, but I've thought through all the issues & discussed them with DH, so he knows what I want (re. pain relief, positioning etc). Don't want to go into the birth with very definite plans, because I want to be flexible - depending on how I am feeling & bubs is doing.

It may be different if you have an OB who you see each time & can discuss options with - I am going through the public system & see different midwives at the clinic (and will see someone completely different for the birth) - so there isn't an opportunity to make plans beforehand with my practitioner.