Let’s lay it on in very simple words. The more detail you provide about your project to your developing team, the less likely your development team will underestimate or overestimate in their estimation. If there is anything about which your specification is unclear about something, you may have to waste time and money later on either to clarify what you wanted or to deal with issues that weren’t obvious at first.
For the developers, having a clear set of requirements from the business and it will let you spend more of your time and budget on your project and less on hammering out details. However, in case you are a non-tech savvy and you want an expert opinion, you can opt to spend extra on an IT consultant to make sure your requirements are not only clear, but also reasonable.