Internally Cubase works at 32 bit float. The recordings are 24 bit, but they are upsampled during the mixing process.
Most VST plugins are 32 bit float.
The downside to mixing down to 32 bit is that you can't play the wav file back in anything other than Cubase, Wavelab or some other editor/DAW that handles those files.
You won't hear any difference between 24 and 32 bit because there is no such thing and 32 bit converters. So the file will have to be converted to to 24 bit on the way out of the DAW.
I always mix down to 24 bit wav files.