And less natural lubrication, which can cause damage to engines that weren't built to handle it. It also has a higher wear and tear rate on rubber seals, and assists with corrosion on the pumps, injectors, etc.
I don't see any value in using 10 so I stick to 50 - a couple guys will throw in a tank of 500 from time to time (I know some recent engines state not to use 500, so in that case, don't) to "flush" the system.
