Concede/Mulligan Option

I often see screen shots with hundreds of concedes but outstanding w/l ratio to go along. Could someone please explain to me why the mulligan option is most normally used?

 

I think my question is a little lost in the translation. I'm asking why do people use that feature? What's the point?

For instance, at the bottom of the main post in this thread they have images linking their wins and losses.

Like this: Why do they have so many concedes? I'm wondering if there's a feature I'm missing that improve win percentages or whatever.

 

Is there a strategic reason to want to keep a rank and not advance?

 

But doesn't a higher rank provide better rewards?