She goes to one of the classifieds portals and enters a search.
She starts viewing search results. Finds your listing.
If the listing does not match well her expectations, she will most likely click away to the next listing in the list, and you have lost her. With the built-in MLS Search, she clicks over to that tab and can search the entire MLS with your Property Search tools. The likelihood that she contacts you about a property is much better!
Very effective: your MLS Search is on many “entry points” on the major portals, where the customers are searching
Under your control: you can choose to embed or not the MLS Search in any one property website.
Aesthetically pleasing: customized background, large photos, slideshow, color schemes
Cumulative exposure: the more you publish, the more “entry points” you have. For ex for 10 listings, on 10 classifieds portals = 100 links where clients can find you. Moreover, once listings get sold, you may keep their websites, thus adding more and more indexed references over time.