When I first started researching my family tree, I did not begin searching cemeteries since I had death certificates. As you move further back in time, there will be a point where you will not find death certificates and this is where newspapers and cemeteries become necessary. You may also want to visit or contact cemeteries so you can enter burial information in your family tree. For my research I did both, I wanted to enter burial information and for other relatives and ancestors it is an alternative source for a non-existent death certificate. I also wanted to document the headstones, as older headstones can become broken, damaged or fade due to the elements.
Usually I can find a cemetery office that can provide a map and plot numbers for my records, this makes cemetery research simple. In other cases, the office has plot numbers, but no map. For instance, one cemetery I visited had the records of where my ancestors were buried, but there was no map and staff had to take me to the location. Even then, several headstones in the area where not maintained and were buried under 10 inches of grass and dirt. The staff unearthed several of the headstones and found that the records they had were slightly skewed. This experience just showed me that you should not always assume a headstone is not present, unless the cemetery office records indicate no headstone (as was my case in at Tulocay in Napa).