What advantages in having access to MLS over realty portal?

[Ricky Stafford]

If an agent sets up a search for you, or you're going through the frontend portal on the realty's website, are there any limitations through this access alone vs. having direct MLS access?

I know obviously Zillow and Trulia are sometimes dated and inaccurate, and shouldn't be relied on, but the searches on a realty's website seem to be 100% up to date. What advantage does the agent have over anyone else?