Certain chords have alternate fingering positions. Sometimes as many as 6 different fingering positions. When one plays a chord that has different fingering positions, does one arbitrarily pick the fingering position that is most comfortable to him/her. Or is there a reason to pick one fingering position over another?
In my limited experience, sometimes it is ease of fretting and ease of transtion into and out of that chord. However, there are times when you want/need to play the chord in a certain position. This is called a voicing of the chord. Sometimes on voicing may fit in the song better than another.
What you're seeing are a combination of positional playing and what is called voicings.
Voicings are different ordering of the tones of a chord. A C major chord has the tones C E and G in it. Any combination of those tones is a C major chord. But you can order those notes many different ways: CEG, EGC, GEC, GCE, etc. Moreover, as a guitar as 6 strings the options become even greater: CEGC, CEGCGE, etc.
Position playing has to do with where you are on the neck of the guitar. If, for example, you are playing a chord in the middle of the neck of the guitar, it is much easier if the chord you are changing too is in that same area of the neck. Moving much higher or lower on the neck will slow your chord change down and unless there's a compelling musical reason for moving it is probably best to limit your voicing choices to that area of the neck.
Musically, reason for choosing one of the other can be quite complex. It can involve which of the chord tones you want in the base to allow your base line to flow, combined with what chord tone or extension you want in the melody line to let the melody flow, combined with what position you are playing, what other instruments you are playing with, your own idiosyncratic tendencies, etc. Ultimately the right choice is going to be made by using your ear.
As you get more advanced, you'll learn that you can drop notes from the chord, you can add notes to the chord, you can substitute one chord for another, and all of this complexity keeps piling up. But at the same time, you'll become more and more comfortable and confident in your own ability to make the right choices for you as a musician, and most of the time choosing the right chord for your tastes becomes fairly second nature.
"The music business is a cruel and shallow money trench, a long plastic hallway where thieves and pimps run free, and good men die like dogs. There's also a negative side." -- HST
