I could see the use in clients using RFPs or RFQs because it saves them time on having to interview companies or firms that may not be qualified. Even though RFPs and RFQs take a lot of time to generate, they also save the firm some time because they don't need to clear their schedule to initially meet with the client that could just turn them down. It is also a two-way street. It is a way for the client to learn more about a firm to see if they want to hire them, but it also allows the firm to learn more about the project to see if they want to get it or even if they have time for such a project. It's good to see an example included in the reading of a RFP outline and to know that a proposal could about 25 pages for a small project, to 50 pages for a large project because our required one was a max of 10 pages. It really helps to put it into perspective. It also helps to know that you should find out the client's "hot button" to know what may be deciding factor in their decision to know what you should stress in the proposal.
Piotrowski, C. M. (2002). Professional practice for interior designers. (3rd ed., pp. 384-387). John Wiley & Sons, Inc.