Good for SEO, not so good for value. But if you develop and get traffic, then could be worth more than many non-hyphenated domains. It really all depends.
But forgetting about traffic and all that and just speaking on the value of only the domain itself and in general, hyphenated domains are worth less than non-hyphenated domains.
In other words, domainnames.com is worth more than domain-names.com. The reason should be obvious. If not, there are many threads about this. One is very new and should still be on the first or second page. Look for the word "hyphenated" not the word "dash".