Rotating keepers, what's it all about?

Can anyone tell me what the policy of rotating goalkeepers is all about in county football?
I think it was Mickey Harte who first employed this tactic with John Devine and Pascal McConnell and Derry manager Paddy Crozier has also continued to rotate keepers John Deighan and Barry Gillis.
This is either very very clever or it's just a crock.
It's not like goalkeepers are overworked even in this day and age and I can't think of any professional side in soccer for example who do this bar Liverpool but their boss Rafa Benitez has a revolving door policy when it comes to team selection.
I just think that a defence always feels confidence when it has a great keeper behind them, and knowing how egostistical even club keepers are, they're never to blame 'it was the flight of the ball, there was an earth tremor, I was unsighted by an eclipse of the sun' you've probably heard them all too, I know that their noses must be out of joint at not being No 1, the only No 1.
It has to have an impact on kick-outs, sweeping up and marshalling the defence.
If you have any views on rotation or any good yarns about your club or county keepers then bang me a note.