The other reason you need to get to know your competition is simply to know who they are. Once you know who they are, you can figure out what they are doing to be successful.
The most important piece of that puzzle is getting to know what they are doing to rank well in the search engines — an essential part of the marketing process. We won't get into this right now but an essential first step is to spend some time narrowing down your competition to 5-6 sites. My company 168MG will handle this marketing research for you if we're hired to develop and market your site. But if you are handling your site marketing on your own go to work analyzing your competition and try to figure out what makes them your top competition.
Once you've done your research, share this list with your web developer or even brainstorm over it with friends and it will surely prove to be highly valuable. You should be able to gauge ease of navigation and why it works well, visual appeal, content depth, search engine friendliness, stickiness, etc.
If search engines are your primary target it might be a good idea to hire a professional SEO company like 168 but regardless, doing proper research on your primary competition will provide you and your developer with endlessly valuable information. If you know your primary objectives, your target markets and you understand how to effectively evaluate your services and your competition, your web site will take you far. Guaranteed.