There is no technical need for auto-reset. It's more a convenience for easy firmware upload. In fact, Melzi has a jumper to turn this off.
If you don't reset, you find the controller in exactly the same state you left it the last time after reconnecting. Or in the just-after-reset state if you cut the power in between. Works fine for printing.
If you don't reset, you find the controller in exactly the same state you left it the last time after reconnecting. Or in the just-after-reset state if you cut the power in between. Works fine for printing.