If you're using a DAW, what you're describing is the equivalent of a copy & paste into a second track, with some panning.
If you're using tape, it's the same concept.
Neither one is the same as a stereo mic technique. Stereo mics take two microphone diaphragms, and position them in order to capture not just the sound, but some directional information in that sound. In order to capture that directional info with a spatial reference frame, you need the two diaphragms. There's some pretty good discussion of stereo mic techniques here, and on the web. Worth a search here and on google...
-mg