changing positioning in fight

[shs101]

I notice not all but some of the "slicker" fighters such as mayweather changes his stance/hand position thru out the fight to do certain things.
If anyone is a fan they can easily tell when he fights he goes from shoulder roll position and then hands up real high sort of a peeka boo guard. Also he'll switch to a more open guard position. More fighters do this but he's a good example off the top of my head while you see tons of other high level fighters stay in one position the entire fight.

What are the pros/cons to fighting like this?

[sugar555]

way you throw your punches as in what angles they come from

[FrenchDeLaHoya]

uses a lean forward then lean back shoulder roll to draw you in. uses the peekaboo when his opponent gets within close range to tighten up his defense. (i do it too when sparring)