Forum Moderators: phranque
1) You don't have to worry about who else appears to be sharing your IP address. It's best if your domain's IP address isn't shared with p*** (adult), pills, and poker sites. Research "bad neighborhoods" as an SEO topic for more information.
2) You can access your server at any time by IP address, regardless of the current DNS setting (domain to IP address mapping), or whether the DNS changes have propagated. This is particularly useful in development or testing, before you "throw the switch" to go live with the domain name.
3) In general, servers with dedicated IP addresses allow you to add subdomains to your domain at will. For example, you could add test.example.com, forum.example.com, blog.example.com, support.example.com, search.example.com, or m.example.com or mobi.example.com (these last two to support mobile devices) in addition to your main example.com domain or www.example.com subdomain.
Jim