Many websites have splash pages on them; it’s a common feature among sites that were designed before SEO knowledge became more commonplace. Splash pages are introductory pages that appear before a website loads, in much the same way that a book or magazine has a cover.
However, websites don’t require covers as you won’t see several websites sat next to each other on a shelf, all vying for your attention. The ‘real’ cover of a website is its SEO. That’s what makes it stand out from the other search results listings, and a website with a splash page will not stand out because it will not rank in the SERPs.
Placing a splash page before your website is the same as building a brick wall in front of your shop. You’re making sure that none of your customers can see it or even know that you’re there at all.
Would you do that? Of course not, then why have a splash page on your website?