As Nick, Elizabeth and Ron explained, the data gathered is just data, nearly irrelevant data. Real estate is a LOCAL affair which requires a real comparison. Comparison requires judgement. As long as sales volume continue at the 1% mobility level, aggregate sites CAN NOT provide actionable data but they do provide ENTERTAINMENT. Aggregate websites will ALWAYS lag the real market.
This same situation allows lenders to suppress market values. With mobility at 1% there simply are insufficient sales in most communities to reach anything other than a 'below market' appraisal. The lender can impose rules on the appraiser that will predictably result in such a discrepancy.
As long as you understand, websites with no accountability for their data, that use words like 'value, ' estimate' Just market value, Zestimate or other misleading terms exist for entertainment purposes for the citizen and advertising purposes for professionals. You should resist adding the perceptions of additional value...it's an illusion.
But it is fun and entertaining.