Some engines are design to use fluid extractor to do oil change, most Mercedes, Audi, previous BMW ... are some of those.
I use Mityvac 7201 to do oil change of my E430, I check the oil level with dipstick the day before to know how much I will extract the next day, I always siphoned all what I measured the day before. Since the bottom of the dipstick tube is at/near the bottom of the oil pan, fluid extractor did a good job of siphon used oil via dipstick tube.
Someone in Mercedes forum tried both ways, first siphoned oil with fluid extractor then open the drain plug and no oil came out of the oil pan, next time he tried to drain oil via drain plug first then used fluid extractor, this time it siphoned several ounces.
But fluid extractor does not do good job with Honda S2000, it siphoned about 4.3-4.6 quarts out of 5 quarts, and about 4.5-4.8 quarts out of 5.2 quarts for LS400. Because oil dipstick tube of these cars are not designed to siphon old oil out with fluid extractor, it's very hard to insert the extract tube to the bottom of the oil pan. You need to try Motive Power Extractor then open the drain plug to see how much oil drain out.
The reason I do oil change with fluid extractor is the cartridge oil filter is on top of the engine, I can do oil and filter change standing up and get it done in less than 30 minutes without a drop of oil on the car or garage.
Picture of E430 engine is below. Lower left corner is oil dipstick, lower right corner is cartridge oil filter holder and above it is the oil fill cap.