First, Single, and all their variants have extension methods on IFindFluent that internally call Limit. This improves performance of some queries and has no impact on the rest. Any and AnyAsync do not have similar extension methods. Because of that I have to add a projection and limit in my client code. Otherwise I would see performance impacts. It would be better if this functionality was built in. Other people using the driver wouldn't necessarily know to do this unless they look at the source code.