Oil analysis on a regular basis is a very valuable tool to keep track of an engine's condition. While perhaps a bit apples and oranges, the various FAA-approved practices of extending an engine's TBO (time between overhauls) has as a primary requirement oil analyses performed at a prescribed interval. This is so that an increase in internal component wear can be detected before the wear becomes a threat to the engine's reliability.
While a one-time analysis does not have the overall value of analyses done over time at specific intervals, it is not totally useless. When we had the boat we ultimately bought hull and engine surveyed, the engine surveyor took oil samples from both engines and the generator and sent them in for analysis. He ran the engines up to temperature, at full throttle, and so on before taking the samples. He told us that a one-time analysis was not going to tell us anything much about the overall condition of the engine, but that it would at least show the contaminant levels in the oil at that particular moment.
The two Lehmans came back clean as a whistle but the Onan had minute traces of metal in the oil. The surveyor's report said that this was kind of the nature of the beast for this engine and it was nothing to be concerned about.
So as others have said in this thread, a one-time oil analysis is not a guarantee of anything and certainly doesn't provide the true value of periodic analyses, which is to show trends. But I think it can at least give a snapshot of the condition of the engine, particularly with regard to illustrating a higher-than-normal level of contaminants.