[nst7]

That will mainly apply to effects like delays, reverbs, etc. It's the same thing as using an aux send on a mono track to a stereo aux track with a stereo plugin. It just allows you to use it as an insert instead.

For example, you can have your mono lead guitar going into a mono delay, or into a stereo delay, where the delays are wider and spread apart. You could achieve that with either method I just mentioned.