In a worn brake system, esp. on a car that sits more than drives, a system where the M/C is level with or lower than the wheel cylenders may have a problem with backflow and air intrusion in the slaves. Residual valves would help with that, but on a daily driver or something where the MC is well over the height of the slaves, shouldn't be much of an issue.
A remote resivior would defiantely negate the need for residuals to prevent backflow, but they are still a nice item for old drum brake systems by helping to reduce the pedal travel needed to fully engage the brakes as the parts wear down. Here's a quick blurb in the
Wilwood brakes webpage.
