A client contacted us for more information about a property he found on Zillow so I pulled it up in the MLS... only to find it had sold last summer! The number one reason you should have your Realtor set up a search for you directly from the MLS is accuracy of information.
Searches directly from the MLS (NOT the same as MLSOnline!) also will let you know if an active listing is sold subject to a contingency, such as inspection (A,i) or third party bank approval of a short sale (A,s)... as well as the number of days it has been on the market (DOM). These searches MUST be set up by a Realtor, the only ones who have direct access. It is NOT the same as MLSOnline, which is a real estate brokerage like RE/MAX or Edina Realty or Coldwell Banker, etc.
Other Buyers are frustrated that by the time they learned about a listing it was already sold. If you wait for it to appear on Zillow or Trulia it may have already been on the market a day or two. Matt Page Group can set up a search for you that automatically searches continuously and will send you an email as soon as a there is a price change or new listing hits the market meeting your search criteria.
Some real estate brokerages, such as Edina Realty, do not send their listings to non-brokerage search engines such as Zillow, Trulia and Yahoo... only agents who contract with those sites themselves have their listings available there. That means you could be missing out on ever seeing some listings if you rely only on those sites.
The MLS also has supplements with additional information you won't find at other sites... supplements such as Seller's Disclosure Statements or city Truth-in-Housing reports. That doesn't mean you should stop looking at other sites, they do have useful information... just don't rely solely on those sites.
I would be happy to set up a Salt Lake City MLS search for you... just email me or text me at 801-450-2579!