if you put your braid on too loosely it can cause wind knots when that section of braid flies off the spool, you can also put more braid if its tighter as opposed to loosely winding it on, also if its loose i find it that splashes of water can seep down into the braid deeper and easier since the braid is loose and has more surface area.

At the start he explains that it's so you're not guessing how much you need. Which is where I go wrong! This takes more time but is a simple solution.

Hi. Most tackle stores can get you the Berkley braids.