32-bit mode with respect to IDE refers to transfers that occur over the PCI bus to the host system memory. PATA is limited to reading 16-bit chunks of data at a time from a drive. If you enable 32-bit mode, the controller will be set to temporarily store the data from one read until the data is available from the next read before mastering a transfer over PCI. So it can collapse two transactions on the IDE side of the controller to one transaction on the PCI side of the controller.
SATA doesn't require a mode like this. It could be said that it's always running in 32-bit mode, I guess -- basically SATA transfers data in serialized packets across the interface to the drive and the controller will just buffer the data until it has enough to send across the PCI bus. There is no need to enable this specifically with a SATA controller.