The flexibility of being able to use either an X or Y axis with no problems when using other machines! I can't think anything that would make me dislike it; however there are times were things don’t always work as you expect them too (e.g., not allowing manual rotation). It's easy enough for anyone new in milling / machining so if someone has never used this type machine control then they may be confused at first but once familiarised everything will just click together quite nicely - especially where turning/routing paths etc have been made easier by having both axes available rather than one only which was previously required e.g. path creation through multiple steps without reordering tools between each step.