With the new patch, you can respec once per difficulty (plus additional respecs if you accumulate the boss drops).
To expand on the information presented in that linked question, do you have to use the respecs once per difficulty, or can I save them up and accumulate 3 respecs by the time I'm on Hell difficulty (plus however many I get through the Cube recipe)?
I'm currently restarting with some friends (I haven't played since the last patch), and I want to know if I'll need to use my normal difficulty respec before I move on to Nightmare.