My team is launching a new site soon.Is it worth blocking spiders from indexing the landing page right now?  What effects will this have on my long term SEO results.  Is this question even relevant? Edit: title changed to reflect real nature of the question.Edit2: great answers below, but in reality I am looking for an answer that directs me to whether the practice of blocking robots pre launch is good or bad for future SEO results.  
Pre-launch Disallow in robots.txt?
seo;web crawlers;robots.txt
If the landing page could allow your competitor's to gain an advantage or steal some of your ingenuity, then YES - BLOCK IT.  However that doesn't mean your page won't appear in search engine results.  It is better to add <meta content=noindex> to each page but more of a pain to add and adjust.This article is great and will help with the details -> robots.txt and effect on SEO