In my 2 years of zbrush knowledge, i have found that u are unable to export a file over 30,000 polys to maya or whatever modelling app you use without maya/max etc crashing. lets say yah wanna send an obj from zbrush to maya and the obj is 100,000 polys onwards, your computers gonna have issues, as for goz i think it automatically lowers the resolution of your mesh to sit comfortably in wahtever app your sending it to.
And yeah man decimation master does lower the polycount. Its even better if the topology is correct also, something im learning now 
Hope this helps man, as i said, im a pure novice at zbrush at the moment 
Im sure theres people out there that can rectify any wrong info i have given (if there is any)