My wife and I use 9lbmono line with 30lb trace and have never been snapped off not even close to being snapped off
everybody always talks about using 20-30lb main line off the beach but in my personal experience that is way too much over kill
my wife is a very inexperienced fisher i have her rod rigged with 9lb and she had no problems
++with the lighter line you can get better distance and less chance of the fish being spooked by it
besides it takes all the fun out of the fight if you can just skull drag in your fish with 20lb main line
The lighter the better thats my opinion