Historically, consideration generally had to pass between parties before there could be a binding contract (eg: a sum of money had to be paid for purchase of the car, even if that sum of money was much less than the true value of the car).  A 2002 case has turned this on its head, particularly in the context of variation of contracts.  This can have implications in the IT sector such as in relation to post-contract amendments, change control and so on.