Can someone please explain the reasoning behind this for me. Thanks.

In order to get a fish out of heavy cover, you don't want to mess around.  You want him out of it as fast as possible before he even has a chance to think about making his escape.

When someone says "Heavy" rod they are referring to its power.  A Heavy rod has a lot of backbone which means when you set the hook and load the rod up, it is really pulling that fish toward you.

A medium power rod cannot do this as quickly and easily as a heavy powered rod.

I hope that made sense.   ;D  

You need a stout rod to be able to quickly extract the fish from the cover once it bites. If you can't do this in time than the fish will tangle you in the cover and you will most likely lose the battle. A stout line like braid is also a big help when fishing cover.

Spend one day in heavy cover with ultra-light tackle and you'll immediately appreciate that equation.

Roger

Spend one day in heavy cover with your ultra-light tackle and you will appreciate that equation.

Roger

lol...Stated much simpler and better than I did.

I figured it would be a simple reason. Thanks guys.