Survey is a proof that there is such property and how big, what have in the property, and as you know, it could change. e.g. without a survey, a legal paper, in which a seller may sell you something does NOT exist. This often happen in remote purchasing.
For example, many years ago, my father's friend in Taiwan bought a land in FL that he never visit and only see the nice picture with Disney World nearby as claimed ...etc, and that legal paper sold him "something does NOT exist".
Lawyer is professional, just like doctor, they perform 100% fact, so a "current survey" by licensed surveyer is all the will believe. The seller may "forget" something change after they bought the property. e.g. My friend bought a house and later remove the swimming pool, and the buyer's banker in the office, never visit the property, how do they know if there is still a swimming pool or not?
So, in general, when you involved multiple parties, paper works is very important. House is not like a car that it is much easier to sell something either not exist or much lesser value than described. (even car is possible, like after sign the title, some bad sellers, often mechenics, would replace cheap tire with the luxury or stereo system with cheaper ones ...etc) This is also possible with buying a house.
I know many cases that before closing, the seller removes many fixtures (often builder professionals or construction contrators), and that often happen in For Sale By Owner case where there is no third party, such as realtor to prove. So last minute walk thru before closing is very important.
The Title search is a more "logical" than "physical" check. e.g. one seller could have sold the same house to "multiple" buyers... How do you know? It happens a lot in PA where legal checking is not very tight.