Remember that we are setting up networks of sites that we may want to sell someday, and the higher value domains are the ones with less syllables, no dashes, are easy to remember, and most of all (if possible) - able to attract “type-in” traffic.
Type-in traffic is traffic from people who simply type a domain in their browser hoping a site is already up on it with the info they are looking for.
That, of course, is the ivory tower of a domain in any niche, but they can still be found. Sometimes it's just a matter of getting it through Domain Registrars like NameCheap or GoDaddy, while other times it may be prudent for you to look into buying them from owners if the price is right.
Lots of people own great domain names, but have no idea what to value them at. Others have sites and traffic on these domains already and have no idea what they're sitting on, are not monetizing and promoting them well or at all, and are ready for someone to offer them $500 or so to take them off their hands.
Putting your site on a current domain with some traffic and some seasoning in the engines is the best possible way to get started way ahead. It's not necessary, but it can give your new site a jumpstart and bring in returns on your investment much SOONER if you can find a good domain already established - as long as you don’t pay too much for it.
Take everything above into consideration before you hastily go out and grab a “phrase domain” with a ton of dashes. Good domain names are part of the asset network you are building and will help command a higher asking price when you are ready to sell the network someday.