Hyphens in a domain name to indicate word boundaries are likely to be of no help to search engines; the search engines probably do an excellent job of finding words in domain names written solid.
All of the search engines have recently spent a lot of time working on Chinese. In Chinese (and some other languages), writing does not normally include word separations. So the technique used to find words is to progress along character by character, looking at a dictionary which has word-frequency statistics and some other information, finding the most-likely words. (This procedure can be carried out with good efficiency.)
This same procedure can be used on solid domain names in any language (using word frequency statistics from the same language) to find the intended words (and occasionally unintended ones).
One well-known kind of example where this may not work is the case of "Example Therapist LLC" using the domain "www.exampletherapist.com". But actually, preferring longer dictionary matches might well give the right result; and on the scale of the search engines, given their huge corpora from which to mine word frequencies, such a procedure would almost always work very well.
Since most people do NOT use hyphens now, already the search engines would need to be able to identify probable word boundaries, using a technique like the one just described. So they may as well use that method for all domain names, even those with hyphens, and treat the hyphens with suspicion, mostly as indicators of low quality.
FWIW, it seems to me that Google is doing better now than it used to at finding domain names containing search words embedded solid within a longer string of characters (in English).
(I've given up all my hyphenated domains, and where I own both the hyphenated and solid versions I've moved to the solid version only. It seems to me that ordinary searchers don't like or trust hyphens, and people are now used to typing in domain names solid. Whether or not this is true, using hyphens seems to be unnecessary.)