[zenpaul]

jiggawatt has a good example.

The thing is that managing inevitable scope changes is an art and a science. Some changes get accepted as part of the project, others are scoped as fixed price updates and others are very hard to scope so may be hourly. In any case this involves identifying the changes, scoping the work, estimating the work, pricing the work and then negotiating with the client to accept the pricing on the change. All of that takes time, often has little to do with the actual development and adds additional risk. That change control is the delicate balance of pleasing the customer while continuing to make money without taking on too much risk.

[agumonkey]

Ok, it's mostly good old business sense in the context of application feature set uncertainty right ?

I understand it's tricky and can be overlooked or swallowed painfully though. Negotiation is a life critical skill.