I really love disc brakes for their effectiveness in inclement weather (rain, sleet, snow) but IMHO hydraulic disc brake systems for bikes are an unnecessary expense with very few returns... a couple of which are that they add a level of complexity and points of failure... not to mention add weight (in most, save for extreme cases). In my experience a properly setup cable disc brake system gives the same level of stopping power and fade resistance as hydraulics yet is less expensive to purchase and less expensive to maintain. One advantage that hydraulics have is that they are self adjusting but IMHO that's a small benefit in comparison to the cost of repairs... and I've had to make a lot of expensive repairs on the ones that came through the shop in the form of fluid contamination causing scoring and failure of lever and caliper o-rings and pistons.