@jessbru99568 totally agree. When I was selling advertising space for a new online publication a lot of the projections were based on very educated guesswork. In those situations I downplayed (just a little). It's always nice to be able to go back to a new client and say you exceeded expectations!

As applicable to business planning I think setting realistic goals help demonstrate your understanding of the market and your current and/or potential position within that market. It's a valuable exercise whether you end up sticking to it or not.