It's important for both the buyer and seller of a transaction to know the importance of a survey and how it can directly effect a transaction.
There are two types of survey's, a location survey and a "pin survey." A mortgage location survey which is most common, is less in-depth and the cheaper of the two. In most cases the title company will take the lead on ordering a mortgage location survey because it is required by the buyers lending institution. Basically, the lender wants substantial proof that all of the improvements on the property (like the house) are located within the legal description boundary lines and the property is properly identified at the county. This protects the buyers investment and the lenders collateral.
The other type of survey is a "pin survey." It is the more typical type of survey people think about when discussing surveys. It is where actual "pins" or railroad pins are placed at the boundary lines of the property. You would want a boundary or "pin survey" completed if you were planning on building on the property or installing an item such as a fence. A "pin survey" is more costly because there is more time that goes into one of them.