Also, sometimes when you record your video's audio with an external mike, you only get one channel of audio (usually only the left). Combining spreads this audio evenly over both channels.

Thank you. However, I could only see left and right audio channels. How to add extra channels to become 5.1 surround project?

Also, sometimes when you record your video's audio with an external mike, you only get one channel of audio (usually only the left). Combining spreads this audio evenly over both channels

In situations like this it is much better to delete the unused channel and use only the "good" channel. It will appear as a mono signal in both speakers.

To add 5.1 surround audio channels, you first create a 5.1 surround project. rtm

Thanks a lot.

The advantage is that if i want them combined, then this function provides that.

Why might i want that? Effectively it produces a mono signal and sometimes that is desirable. My biggest use for mono is when producing spoken word audio files for internet delivery and i want the files to be as small as possible. Switching to mono allows files half the size of stereo files at the same quality/compression level.

You and others may have other reasons for wanting mono, or you may not. As with most features and functions though, it's there for use when it is helpful/necessary/desired. If it's not advantageous for some reason then don't use it.