At one end of the market, there may be small groups or individuals making submissions to local or state government agencies. These clients often have little or no experience in preparing such submissions and lack personnel with the requisite skills to prepare a winnable bid. The quality of the submission is the main consideration here.
For larger project submissions, there may be consultants who would benefit from an independent eye going through the project documentation or report before presentation, checking both the quality and completeness of the submission. Completeness requires that all the terms of reference are addressed and that other submission instructions are addressed and checked off.
Such reviews are usually done in house but in house reviewers may be too close to a project to give an independent assessment. The opportunity cost of not winning a bid may be the prime consideration in this case. Many a project has been lost because of a missing signature on the application.