If you are recording a VO, then just record mono. You only have one mouth, there is no point in taking two channels to do what one will do. It's also a smaller file size. You can select whether a channel will be recorded in mono or stereo on the track being recorded on.
If it's a stereo recording, such as a stereo instrument or mic, just record it stereo.
If you have a mono instrument, mono mic, and record in stereo anyway, just right click the audio, select 'Channels' and then choose Combine. It will become a mono track, but file size won't change, because you haven't altered the original audio.
When it's mixed down/rendered, it will feed equally to both channels.