Babystepping as marlin implement it sends a specified number of extra step pulses to the z motor driver per turn of the encoder wheel. So it's coordinate-system independent, instant and in the latest versions theres a readout on the Lcd to say how many millimeters you moved, which you can use to set a permanent z offset in firmware or your slicer.
This is what we need really, it's tried and tested. If reprap firmware wants to steal a march on marlin then and option to save the offset for the next print would be a wonderful addition. Perhaps into the new configuration override file.
I accept that if you have a really precise, reproducible printer and you don't change it much then you set the z offset once and then just use it. But if your printer isn't that tight, or you're testing things or change nozzles a lot, or hot ends this can save you hours and lots of filament.