I'm building a job board, but I keep wondering if it needs a landing page? If people surf to the site, they immediately get to the 'job search' page. Should I first explain what the site does and add a CTA or is this self-explanatory?
You will have a landing page no matter what you choose, as there has to be a default page. Whether you choose to optimise that experience or not is the question.
Even if the main use of the site is the search, you still should have a planned landing page. You can choose to make the search the focus of that page (like hipmunk). If you have content you should use the landing page to provide customers with content that you think they will be interested in, or the content that you would like to promote.
Every website should have a centralized page, this would allow the user to navigate to "Browse" other pages. This would also give them more reason to go back to your site in the future.
A job board could be easy to create a useful homepage. Possibly integrating a feed of most recent job posts, and sortable by category or job type?
Yes, you should explain what your site does! Nobody ever complained that a web site was made too simple for them to understand.
This goes double for job boards -- honestly, I'm sick and tired of dealing with crap boards, crap recruiters, and crap jobs posted by crappy HR. If your service isn't an improvement over other job boards and sites in at least one aspect, whether it's that it serves a specific niche, or it includes a special way of visualizing my resume in a way that I think serves my interests, or otherwise promises something that other sites can't deliver on (Hint - Stack Exchange Careers 2.0 allows me to plug in my SE accounts, which I like!), I'm going to be hesitant to give my information over to yet another job board.
You have to tell me what that aspect is somehow... so you may as well use the home page as a landing page to do it!
A Landing Page as an introduction to your site...
Don't do it.
For everyday use, Landing pages are a thing of the past. Traditionally, they were like the loading dialog of a software application. Some designers even believed that using Flash would enhance this paradigm. The landing page is a dated concept that serves little purpose, and usually ends up having almost no SEO value.
The 'home page' of a site, on the other hand, is a place that should act as the 'lead-in' to everything on your site. It serves to funnel different customers into areas of your site that may be of interest. Not all traffic to your site will come from Google or similar, so you need a way to deal with organic traffic that explains your purpose. If you don't grab these users' attentions within the first 10 - 20 seconds, they may be gone forever.
It is a place to announce news and new content, and should have a prominent search right on the page where it cannot be missed. Worse than a landing page, is a home page that leaves your intended audience confused about the purpose of the site.
Landing Pages for promo campaigns
Do it right.
You should try to use a landing page for every inbound advertising campaign you operate. You might have multiple offers or setting up promotional offers for different user segments and your homepage can’t deal with this level of message differentiation without becoming crazy. The style and effectiveness of your inbound marketing will also vary according to the source (PPC, email, organic, social media, display banners), so you should try and provide a relevant experience to each input funnel.