It is not important at all IMO, unless maybe you are salt water fishing or flathead catfishing. I have never seen a fish take drag on a 12# system tightened all the way down. And for the guys that will step in here and say “its for when you are fishing in weeds”, if you have a bass dive down into the weeds, wouldnt it be just as easy to put your thumb on the spool to pull him out? I dont see where it would be necessary for a 20lb+ drag system.
Watch a pro frog fishing and you will see the first thing he does when that fish turns its head, after getting the wrath of satin hook set, is to put his thumb on the spool to turn his head and get him coming the right way.