When trying to split a print into multiple processes, the Preview Mode displays the visible layers. "Layer Modifications" in the Advanced tab allows mm as input. Allowing layer input to Layer Modifications or displaying Z height of visible layers in Preview Mode would make things easier. Both options would be great, but one or the other would be nice.
Another thing that would make things run more smoothly is if there was an option for a warning when "Layer Modifications" prevents the entire model from being printed. An example for when a warning should display would be if I was printing a 50mm cube and I left it set for a single process for 0-40mm from a previous multi-process model. Another example would be if I had a process set to print 0-24mm and one set for 26mm+(typos happen!). The first example is sometimes obvious, but if you're printing a cylinder, it's difficult to tell visually in the Preview Mode. You don't find out until your cylinder is shorter than expected. The second example is much more obvious on all prints, but mistakes happen and a simple.