Mr.Trump Jr good question,
Remember in the early days of the web alot of .com names were available and you could probably get thedogcookiediet dot com.
As the internet grew alot of names got taken.
So you have a brillian idea and want to register your domain name, but to your suprise someone is already using that name.
The next logical step is to create the same name with hyphens or a different variation thereof.
I have personally never seen a domain name with underscores in. However I personally use hyphens in a couple of my domain names and hyphens and underscores in my filenames.
Hyphens is very good for SEO purposes. However if you have a very long name like one of my websites
www.how-2-make-a-website.com it might not be easy to remember or type in the web browser. A word like howtomakeawebsite is easier to remember. The reason why I chose that domain name is, because all the one word domain names was already taken.
Amazingly my website url
www.how-2-make-a-website.com rank top in the all the major search engine SERPS from 100s of millions other websites and sometimes billions of websites for certain competitive keyword(s).
So the lesson to be learnt is that the kiss (keep it simple stupid) principle is the best, but for SEO purposes hyphens and underscores is good.
