to lead leap forward with racket foot or non racket foot

To lead/ leap forward with racket foot or non racket foot


Hi guys, im a beginner in badminton, and as per the title, i have several questions about returning low serve. I happened to watch professional doubles game i.e Hendra/ Ahsan and Kevin/Marcus, and i seemed to notice Ahsan and Kevin tend to lead / leap forward with his non racket leg when returning the serve, while Hendra and Marcus tend to use his racket leg to take the shot.

So my questions, are there no guidelines about this matter? what is the advantage and disadvantage of either?
Oh, and sometimes i saw professional switch their leading leg when returning the low serve, are there a conditions or certain shots to switch their lead racket leg ?

I’ve tried asking my advanced friends about this, but got no clear explanation about this matter. Hope you guys can give the answer im looking form.
Thank you. And im sorry for my bad English.