why can't you use park tool shift cable cutter to cut hydraulic cable I was going to use my parktool cable cutter on the hydraulic cable for my reverb.
 I would potentially service my hydraulic shimano disc brakes cables if I ever need to. But another thread has said you shouldn't. if it can cut metal why not hydraulic cable
The comments OraNob and Batman said are spot on. A cable cutter uses shear force (focused crushing) to cut through the metal wound wires in a cable housing but still requires some clean up because of this. This is why you need to go back and reform the inside wires with an awl and clean up the edges with a file or sanding pad. A plastic hydraulic line can easily be cut with a sharp blade or razor. A brake line can not, you could cut it but it will mar up the blade and deform the cable creating more friction when the cable is reintroduced.

You can't sand a hydraulic line because it will introduce particles into the fluid which could then lodge and build up in the moving parts of the brake system.

Also the plastics that are used in hydraulic cables don't do well with being smashed and reformed and could hairline crack if crimped and then reformed. If it did crack you would have to start over and try again, a vicious cycle. All it takes is a tiny crack to allow air into the system and turn your brakes to mush. 

The hydraulics lines are made to perform under pressure, pun intended, and doing the above creates a weakened area that may lead to cracking at the fittings. They won't be easily visible but could allow air to slowly be introduced to the system.

When I have serviced my brakes, I cut the hydraulic line with an X-acto knife, a razor would work equally well. I put it on a hard wooden work desk that has a 90º angle cut into it. This way i find it very easy to cut a straight line in the hose. I used a sawing motion to be sure that I wasn't crushing the housing at all but this may be overkill. If you cut at an angle it can also cause a bad fitting connection that may lead to air in the system.