I work on a large motor yacht and we do a fair amount of oil sampling not only in engines but things like windlasses, oil bath shafting, etc. An occasional oil sample might be of some use but for the most part I wouldn't worry too much. Probably the most important number on an oil sample for our engines would be fuel dilution or how much gasoline is making it into the oil. Too much fuel in the oil can cause increased wear particularly on the cylinder walls and is also an indicator that your ignition system isn't up to snuff, your injection pump needs calibration or in the worse case your injection pump needs rebuilding because fuel is leaking past the pistons on the injection pump.