Scheduling conservatively usually results in a more reliable launch date. The client doesn't have full authority to make decisions. This is one of the deadliest problems in the project-risk minefield. The business model hasn't been settled. Approach with caution any projects in which the client hasn't defined their business model, especially if it's an e-commerce application or an extranet project.
Development begins before the planning is done.
Putting your designers and programmers to work too early will only mean more revisions, headaches, and lost time. The project is understaffed . From what I've seen, the proportion of work to staff in web development groups virtually guarantees project understaffing. While it's tempting to try to squeeze in yet another project, be aware that the success of the entire pool of projects will be affected. Team members don't have the skills necessary to complete their tasks.