Splash pages are pages which come first before the main page of your website. These are use to grab the attention of your visitor and the content may be remarkably different to your website. The chief concern is the essence of these pages to the website regarding search engines page rank.
Aside from the fact that many website owners and users find splash pages annoying, it will also have a significant influence on SEO ranking.
Search engines have their own algorithm to compute websites and check what is the most relevant to words typed in the search box. These would qualify a site based on title, content, keywords and Meta tags. These pages, on the other hand, does not possess most of this part of a website, making your site on the lower rank.
These pages do not have any content or keyword rich phrases. These are requirements for ranking, but the lack in a splash page would prevent spiders to crawl to the main site and would not be able to perform the job.
What these pages have are banners or links that will lead to another page or window, making it difficult to be indexed. This will make the search engine assume that your page has the weightiest content. This can give the engine useless content of your site resulting them to rank your website unusually low.
You are able to change, and it is necessary to change it regularly. This is for engine to presume that they are updated and that they may index your site.
If you want your site to get a higher page rank, do not attempt to create a page for your website. However, if you want to give it a try, do a thorough research for any search engine optimized pages.