...they want to show something on landing/entrance page - www.domain.com/welcome before the visitors get into the home page i.e. www.domain.com
Just came across this... not sure my reply is timely enough to be of help... but, both from the SEO and from the usability point of view, this is not a good idea.
Very briefly (and to oversimplify)... for SEO, you will be costing yourself credit on inbound links. Most inbound links to a site will naturally occur to www.domain.com. But, with the splash page, you will be promoting a different page... www.domain.com/welcome. So, there will a likely splitting of your inbound link vote, with no benefits.
You don't describe what the navigation structure would be from /welcome ...whether it's an image-only splash page or whether it does have navigation to the rest of the site. Again, I envision only negative effects in whatever you do.
From the user point of view, "Welcome" pages usually slow the visitor down. I think they were very common in the US in the late 90s, but they've fallen from use for good reason. While there's something gracious and well-mannered about saying "welcome" to new visitors, this loses its effect in the modern internet, if every site "welcomes" every visitor. The welcome message on a site, IMO, has become an old-fashioned cliche.
I should add that I've boosted the rankings and traffic of many sites considerably simply by eliminating "welcome" pages set up as you describe... though usually that's not all I do when I encounter this kind of situation. I've never considered going in the other direction. Effectively, in adding a welcome page, you'd be undoing your site's default url "canonicalization", and that simply doesn't make sense.