Well as with anything else, the more you know about something the better you can usually use it to get the most out of it. In this case it might be important to know if you have a cardioid mic if you do voice-overs and would like to get a deep, bass-y sound out of your voice without having to futz with EQ or other audio effects. With a cardioid all you have to do is get your mouth closer to the mic and take advantage of the “proximity effect.” Or maybe the sound has too much bass. Then you’d know that getting a bit further from the mic will make the audio sound even less bassy. This knowledge can be really handy.
Maybe you want to do stereo recording but don’t have a stereo mic, or don’t have two of the same model of mic. If you have a cardioid mic (most mics) and one capable of figure-8 (or bi-directional mic) recording, you can make use of mid-side stereo recording.
Find out about all these things in the latest article at Home Brew Audio: http://www.homebrewaudio.com/directional-and-omnidirectional-microphones-what-are-they-good-for