The problem with Zestimates is they use a radius around the house of properties. We know they don't compare condition or view or specific location (just a general condition).
Even the CEO of Zillow had his Zestimate waaayyyy off. His Zestimate was on the order of $1.6M and his home sold for approx $1.050M back in March 2016 - see this link for details: https://appraisaltoday.com/2016/06/01/zillow-ceo-sold-home-60-percent-zestimate/
Zestimates are of the automated valuation model (AVM) variety - and those models are proprietary so we don't know exactly which "comparables" were used. Some of the AVM's will disclose their comps (RPR for example) and you can eliminate the non-comparable comps. Even so, these AVM's are notoriously inaccurate.
Appraisals are much more accurate - but they will vary too. It depends on the use like one of the others pointed out. His LTV was low so the appraisal was a quickie 
In my experience, I would totally ignore the Zestimates. If you don't want to pay for an appraisal and are just curious, contact your Realtor for comparable sales. That will give you a much better idea of value than the Zestimate.